한국방사선산업학회

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INTRODUCTION

When a cell is subjected to ionizing radiation (IR), many

chemical reactions are induced, eventually leading to

lesi-ons which can express themselves in a variety of

bio-logically significant changes (von Sonntag 1987). It has been

known for many years that exposure of living systems to IR

results in the immediate formation of essentially three

diff-erent free radicals, the hydroxyl radical (OH

∙), the solvated

electron (e

aq-

) and the H-atom thorough the radiolysis of

water. These primary water radicals can be converted into a

series of partially reduced species collectively known as

reactive oxygen species (ROS). These include superoxide

(O

2∙-

), hydrogen peroxide (H

2

O

2

), hydroxyl radical (OH

∙)

and peroxyl (ROO

∙) and alkoxyl (RO∙) radicals which are

believed to induce oxidative damage in various cellular

compartments such as DNA, proteins, and lipids that

con-tribute to the biological effects of radiation (von Sonntag

1987; Riley 1994; Spitz et al. 2004). It is now universally

accepted that the DNA represents the most critical target of

IR (Diehl 1995). Ionizing radiation produces a wide

spect-rum of DNA lesions, such as: base damage, sugar damage,

single strand breaks (SSB), double strand breaks (DSB),

DNA-DNA and DNA-protein cross links (Symons 1994).

These lesions rapidly results in recruitment of DNA repair

machinery to sites of damage, as well as triggering multiple

signaling pathways (Amundson et al. 2003).

Because DNA microarrays containing oligonucleotide or

cDNA probes can measure the expressional levels of

thou-sands genes simultaneously through a single hybridization

experiment, several groups have used microarrays to study

the response to IR. Transcriptional induction of DNA repair

genes, immediate early genes, and a variety of cytokine and

growth factor genes have been proposed as the mechanisms

─ ─ 111 ──

Gene Expression Profiles Following High-Dose Exposure to Gamma

Radiation in Salmonella enterica serovar Typhimurium

Sangyong Lim, Sunwook Jung, Minho Joe and Dongho Kim*

Radiation Research Division for Biotechnology, Korea Atomic Energy Research Institute,

Jeongeup 580-185, Korea

Abstract -

- Microarrays can measure the expression of thousands of genes to identify the changes

in expression between different biological states. To survey the change of whole Salmonella genes

after a relatively high dose of gamma radiation (1 kGy), transcriptome dynamics were examined

in the cells by using DNA microarrays. At least 75 genes were induced and 89 genes were reduced

two-fold or more after irradiation. Several genes located in pSLT plasmid, cyo operon, and Gifsy

prophage were induced along with many genes encoding uncharacterized proteins.While, the

expres-sion of genes involved in the virulence of Salmonella as well as metabolic functions were

decreas-ed. Although the radiation response as a whole could not be illustrated by using DNA

micro-arrays, the data suggest that the response to high dose of irradiation might be more complex than

the SOS response.

Key words : DNA microarrays, Gamma radiation, Radiation response

* Corresponding author: Dongho Kim, Tel. +82-63-570-3140, Fax. +82-63-570-3149, E-mail. [email protected]

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by which cells survive after IR in mammalian cells (Tusher

et al. 2001; Heinloth et al. 2003; Rieger and Chu 2004).

However, transcriptional responses to IR can vary in

dif-ferent cell types and at difdif-ferent radiation doses or time

points following radiation (Short et al. 2007). Gene

induc-tion after the exposure of the Arabidopsis plants to IR has

been recently reported (Kim et al. 2007). In bacteria, array

technology applied to a special bacterium, Deinococcus

radiodurans best known for its extreme resistance to IR,

and it has been used to identify genes that are associated

with radioresistance of D. radiodurans (Tanaka et al. 2004;

Joe et al. 2008), because most vegetative bacteria have

been considered as targets of IR-sterilization. Although

many features of the damage response are conserved from

micro-organism to humans (Cromie et al. 2001), the

res-ponse in bacteria will have features not found in

eukar-yotic cells.

In this study we have analyzed changes in gene

expres-sion in Salmonella Typhimurium using microarray analysis

after a relatively high dose of radiation, 1 kGy.

MATERIALS AND METHODS

Bacterial strain and growth conditions

Salmonella enterica serovar Typhimurium SL1344 was

cultivated aerobically at 37

�

C in Luria-Bertani medium

containing 1% bacto-tryptone, 0.5% yeast extract, and 1%

NaCl. A stationary-phase culture that had been grown

overnight with shaking was used as a stock culture.

Irradiation

Two 250-ml Erlenmeyer flaskscontaining 50 ml of fresh

medium were inoculated with the stock culture at 1 : 100

and then were incubated aerobically to exponential phase

for 4 hr. After these cultures were transferred to a 50-ml

coni-cal tube (Falcon), one was irradiated at room temperature

and the other was not irradiated. Each culture was

re-transferred to a 250-ml Erlenmeyer flask, incubated for a

further 1 hr, and cells were harvested by centrifugation for

RNA isolation. Gamma irradiation was performed using a

60

_{Co gamma irradiator (point source; IR-79, AECL,}

Otta-wa, Ont., Canada). The source strength was approximately

14.8 PBq at a dose rate of 2 kGy h

-1

_{the actual doses were}

within

±2% of the target dose. The applied dose of

irra-diation was 1 kGy.

Probe preparation and hybridization

Total bacterial RNA was isolated using SV total RNA

isolation kit (Promega) according to the manufacturer’s

instructions. The quality and integrity of the prepared total

RNAs were confirmed with the use of an Agilent 2100

bioanalyzer (Agilent, Palo Alto, CA, USA), and by

spectro-photometry. A total of 50

μg of RNA with 3 μg of random

hexamer dissolved in 29.5

μl of nuclease free-water was

denatured at 65�

C for 10 min and then placed on ice. After

addition of 6

μl of 0.1 M DTT, 12 μl of first-strand buffer (5

×), 1.5

μl of dNTP mix (25 mM dATP, 25 mM dGTP, 25

mM dCTP, 10 mM dTTP), 4

μl of reverse transcriptase

(Superscript II

�

_{Invitrogen), 2}

μl of RNasin (Promega) and

4 μl of either Cy3- or Cy5-conjugated dUTP (Amersham

Biosciences), the labeling mixture of 60

μl was incubated at

42�

C for 2 h and then supplemented with 2

μl of Superscript

II at the end of the first hour. Each probe was denatured

with 10

μl of 1M NaOH and neutralized with 10 μl of 1 M

HCl, followed by purification with a PCR purification kit

(Qiagen) and concentration with speed vacuum drier. Each

probe separately labeled with Cy3 or Cy5 was resuspended

in 20

μl of distilled water, respectively. Equal volumes of

labeled probes (each 20

μl) from non-irradiated and

irradi-ated cultures were mixed with 40

μl of 2× hybridization

solution consisting of 50% formamide, 10× SSC and 0.2%

SDS and denatured by boiling for 5 min. Probes were

hy-bridized simultaneously to a chip at 58�

C for 16 h in a

hybri-dization chamber.

Scanning and data analysis

Details concerning the construction and characteristics of

the Salmonella microarray used in this study have been

described elsewhere (Porwollik et al. 2004). Briefly, 97.5%

of all 4,498 genetic elements annotated in S. Typhimurium

LT2 are represented in triplicate on the array, as are 104 of

the 109 annotated genetic elements of the virulence

plas-mid pSLT. Scans were performed with a GenePix 4000B

scanner (Axon Instruments, Union City, CA) by using the

ScanArray 2.1 software (Packard BioChip Technologies).

Signal intensities were quantified by using the GenePix 3.0

software (Axon Instruments, Union City, CA).

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Normali-zation of gene expression by a LOWESS regression was

applied for 6 data which were obtained from two biological

replicates. The genes were considered differentially

expre-ssed when the logarithmic gene expression ratios were

more than a 2-fold difference in the expression level.

Stati-stical significance of the data was determined by Student’s t

test. P-values less than 0.01 were taken as statistically

signi-ficant.

RESULTS AND DISCUSSION

To examine the changes in gene expression of S.

Typhi-murium following a dose of 1 kGy, we used a DNA

micro-array that includes 4,498 ORFs from Salmonella

Typhi-murium LT2 and 104 ORFs from the pSLT virulence

plas-mid (Porwollik et al. 2004). Total RNA was purified from a

sample taken 1 h after irradiation, and used to make cDNA

that was labeled and hybridized to the microarray. To

control for irradiation-independent changes, total RNA

pre-paration from a non-irradiated sample was also performed

(see Materials and Methods). Of all genes showing a

stati-stically significant expression ratio (p

⁄0.01) of at least

2-fold change relative to non-irradiated counterpart, 75 genes

were induced and 89 genes were reduced by irradiation

dose of 1 kGy. The lists of the genes up- and

down-regulat-ed by irradiation are presentdown-regulat-ed in Tables 1 and 2,

respective-ly. An overview of the genes was obtained by defining

fun-ctional categories of genes based on the data of The

Insti-tute for Genomic Research (TIGR; www.tigr.org/tigr-scripts

/CMR2/CMRGenomes.spl). Among the genes whose

ex-pression was altered by irradiation, nearly all functional

groups are represented. Genes involved in cell envelope,

cellular process, DNA metabolism, energy metabolism,

protein synthesisand regulation of gene expression showed

the modified expression following exposure to a relatively

high dose of irradiation, 1 kGy (Tables 1 and 2). However,

it is unlikely to describe systematically the whole response

to this dose of irradiation, because many (about 54%) of the

altered genes were assigned to putative genes.

The central dogma of radiobiology was established that

radiation-induced DNA lesions and their repair determine

the biological effects observed at the cellular level (von

Sonn-tag 1987; Riley 1994; Spitz et al. 2004). The cell including

bacteria responds to this stress by upregulating the

expres-sion of several genes that function to repair DNA leexpres-sions,

restore replication, and prevent premature cell division.

These changes in gene expression in response to DNA

da-mage produced by ultraviolet (UV) or other DNA damaging

agents have been collectively termed the SOS response.

The SOS response is a co-ordinated increase in the level of

expression of about 30 unlinked genes induced by DNA

damage, whose expression is regulated by the recA and

lexA gene products (Sutton et al. 2000). Changes in gene

expression after treatment of Escherichia coli with DNA

damaging agents such as mitomycin C (MMC) or UV

irra-diation were assessed using DNA microarray. Although

gene expression response patterns observed in the three

studies were very different, 5 of SOS genes (sulA, recA,

recN, dinD, and dinP) were heavily induced via

LexA-dependent manner in all three studies (Courcelle et al. 2001;

Khil and Camerini-Otero 2002; Quillardet et al. 2003). In

our experimental conditions, however, we didn’t observe

upregulation of many of the SOS-inducible genes, except

for yjiW (Table 1).

The expressed SOS functions not only repair the DNA

damage but also drive the lateral spread of mobile genetic

elements, which are range from prophage to integrative and

conjugative elements (Aertsen and Michiels 2006). It was

previously found that the gene transcription of Gifsy-1 and

Gifsy-2, which are also resided in S. Typhimurium SL1344

genomes, was repressed by overproduction of the LexA

protein and induced by hydrogen peroxide and MMC

(Bun-ny et al. 2002; Frye et al. 2005). Among the 10 genes which

displayed the highest expression level following irradiation

in our result, we could find the genes belong to Gifsy

pro-phage. In addition, some tra genes associated with

conju-gative transfer of Salmonella pSLT plasmid were induced

by approximately 2.5-fold relative to non-irradiated

coun-terpart (Table 1). Together with the strong induction of

ibpB (

~4-fold) known to be induced in a LexA-dependent

manner (Courcelle et al. 2001), our result suggests that the

SOS response can be induced by 1 kGy of gamma irradiation

as expected, but the SOS-inducing signal/mechanism

gene-rated by this dose of radiation appears to be different with

the typical signal activated by exogenous DNA damaging

agents such as UV irradiation or MMC.

The discrepancy between the gene expression response

patterns is also observed in the previous studies. In the

study by Courcelle et al. (2001), 20 of the 27 known

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LexA-Table 1. Genes with increased expression following gamma irradiation

Gene number Gene symbol Possible function Ratioa

Amino acid biosynthesis

STM3601 Putative phosphosugar isomerase 3.91

STM4121 argC N-acetyl-gamma-glutamylphosphate reductase 2.17

Biosynthesis of cofactors, prosthetic groups, and carriers

STM0794 bioB Biotin synthetase 2.03

STM0795 bioF 7-keto-8-aminopelargonic acid synthetase 2.04

Cell envelope

STM0446 bolA Morphogene; putative regulator of murein genes (BolA family) 2.18

STM0780 Putative outer membrane or exported 2.25

STM1632 Putative inner membrane protein 2.23

STM3115 yqgA Putative inner membrane protein 3.68

Cellular processes

PSLT075 traJ Conjugative transfer: regulation 2.62

PSLT077 traA Conjugative transfer: fimbrial subunit 2.68

PSLT080 traK Conjugative transfer: assembly 2.65

PSLT101 traG Conjugative transfer: assembly abd aggregate stability 2.75

STM3808 ibpB Small heat shock protein 4.06b

STM4055 sodA Superoxide dismutase, manganese 3.21

DNA metabolism

PSLT003 repC DNA replication 2.43

PSLT006 repA DNA replication 2.84

STM3648 yiaG Putative transcriptional regulator 4.38

Energy metabolism

STM0169 gcd Glucose dehydrogenase 2.13

STM0440 cyoD Cytochrome o ubiquinol oxidase subunit IV 2.85

STM0441 cyoC Cytochrome o ubiquinol oxidase subunit III 3.07

STM0442 cyoB Cytochrome o ubiquinol oxidase subunit I 3.23

STM1457 Putative respiratory-chain NADH dehydrogenase 2.07

STM3600 Putative sugar kinases, ribokinase family 3.53

STM4401 ytfG Paral putative reductase 3.23

STM4436 Putative endonuclease 3.39

STM4485 idnK D-gluconate kinase, thermosensitive 3.30

Fatty acid and phospholipid metabolism

STM4236 dgkA Diacylglycerol kinase 2.04

Hypothetical proteins

STM1838 yobF Putative cytoplasmic protein 2.25

STM4523 yjiW LexA regulated, putative SOS response 2.18

Mobile and extrachromosomal element funcitions

STM1007 Gifsy-2 prophage 3.87

STM1033 Gifsy-2 prophage; resembles Clp protease 4.03

STM1036 Gifsy-2 prophage: probable minor tail protein 5.16

STM1041 Gifsy-2 prophage; probable minor tail protein 2.11

STM2760 Putative integrase 4.26

Protein fate

STM0632 ybeC Putative Sec-independent protein secretion pathway component 2.20

STM3144 hybF Putative hydrogenase expression/formation protein 3.43

Protein synthesis

PSLT047 Putative cytoplasmic protein 4.47

STM0391 yaiE Putative cytoplasmic protein 2.12

STM0727 Putative cytoplasmic protein 2.23

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regulated genes had been found to be induced by UV

irradiation and this result is good agreement with another

similar study that analyzed the gene expression after UV

irradiation (Quillardet et al. 2003). However, in the study

that used MMC as a DNA damaging agent instead of UV

irradiation, only a small number of known LexA-regulated

genes were induced by MMC (Khil and Camerini-Otero

2002). The Gifsy prophage was reported previously to be

strongly induced by MMC (Smith et al. 1991), while that

was inefficiently induced by UV (Bunny et al. 2002). In

addition, the responses of operons encoding genes involved

in protein synthesis, carbohydrate transport,

aerobic-ana-erobic metabolism, and cell surface structures to hydrogen

peroxide and MMC were significantly different (Frye et al.

2005). Similarly, MMC caused an increased expression of

type III secretion system (TTSS) that is necessary for

form-ing attachform-ing and effacform-ing intestinal lesions (Mellies et al.

2007), while gamma radiation reduced the transcription of

pipA, pipB, and sirC that are involved in Salmonella

patho-genicity islands (SPI) encoding TTSS in our experiment

(Table 2). The above result is compatible with our previous

result of the down-regulation of SPI genes after gamma

radiation (Lim et al. 2007). Given this background, it is

unlikely that all of the various types of DNA damaging

agents will cause equally the final cellular effects that are

of interest for radiation biology.

Therefore, the striking difference between our work and

those cited above could be possibly explained by the

qua-lity of DNA lesions. A key difference between ionizing

radia-tion-induced damage and those produced by other chemical

oxidizing agents is that a range of damage products are

locally clustered on the DNA. Ionizing radiation forms the

clustered damage, two or more elemental lesions (base

modification, abasic site, and single-strand breaks), within

about one helical turn of the DNA (Prise et al. 1999;

Suth-erland et al. 2000; Jenner et al. 2001) Although DNA

dou-ble-strand break has been predicted to be important lesions

in terms of biological effectiveness, they may simply not be

Table 1. Continued.

Regulatory functions

STM1311 osmE Transcriptional activator of ntrL gene 2.83

STM2268 micF Regulatory RNA 2.29

STM3893 9S Regulatory RNA 2.31

STM4117 yijO Putative regulator (AraC/XylS family) 4.67

Transport and binding proteins

STM2481 acrD RND family, aminoglycoside/multidrug efflux pump 2.16

STM3790 uhpA Response regulator of uhpT operon (LuxR/UhpA family) 2.33

STM3847 yidY Putative MFS family tranport protein 2.00

STM4075 ydeY Putative ABC superfamily, sugar transport protein 3.38

STM4195 Putative Na++_{-dependent transporter} _3.84

Unclassified

PSLT048 tlpA Alpha-helical coiled coil protein 2.52

STM2746 Putative excinuclease ATPase subunit 4.85

STM2805 nrdH Glutaredoxin-like protein; hydrogen donor 2.13

STM4281 nrfE Formate-dependent nitrite reductase 3.72

Unknown function

STM0240 yaeJ Putative-tRNA hydrolase domain 2.16

STM0841 ybiU Putative cytoplasmic protein 2.04

STM1146 ymdA Putative periplasmic protein 2.24

STM1269 Putative chorismate mutase 2.21

STM1869 Homology to phage-tail assembly proteins 2.22

STM1881 yebF Putative periplasmic protein 2.72

STM2116 wzc Putative tyrosine-protein kinase in colanic acid export 3.86

STM2119 yegH Putative inner membrane protein 4.38

STM2128 ego Putative aldose transport system, ATPase component 7.09

STM2795 ygaU Putative LysM domain 3.96

STM2983 ygdI Putative lipoprotein 2.93

STM3007 ygdR Putative POT family, peptide transport protein 2.30

STM4449 Putative helix-turn-helix protein, copG family 2.18

a_{The ratio is the fold increase in mRNA level in irradiated culture compared to control culture.} b_{Ten genes whose expression is most highly altered by irradiation are indicated in bold.}

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Table 2. Genes with reduced expression following gamma irradiation

Amino acid biosynthesis

STM0002 thrA Aspartokinase I 0.44

STM3877 asnA Asparagine synthetase A 0.42

Biosynthesis of cofactors, prosthetic groups, and carriers

STM0756 nadA Quinolinate synthetase, A protein 0.48

STM1165 grxB Glutaredoxin 2 0.44

STM1450 pdxY Pyridoxal kinase 2/pyridoxine kinase 0.17

STM2030 cbiT Synthesis of vitamin B12 adenosyl cobalamide precursor 0.36

STM3206 folB Dihydroneopterin aldolase 0.48

STM4012 Putative coproporphyrinogen III oxidase 0.14

STM4159 thiH Thiamine biosynthesis enzyme 0.32

STM4163 thiE Thiamine phosphate synthase 0.31

Cell envelope

STM0026 bcfF Fimbrial subunit 0.32

STM0157 yacH Putative outer membrane protein 0.46

STM0302 safD Putative fimbriae subunit 0.38

STM1155 htrB Lauroyl/myristoyl acyltransferase involved in lipid A biosynthesis 0.18

STM2107 wcaH GDP-mannose mannosyl hydrolase in colanic acid biosynthesis 0.50

STM2771 fljB Flagellar synthesis: phase 2 flagellin (filament structural protein) 0.33

STM3036 Putative inner membrane protein 0.09b

STM3372 mreD Rod shape-determining protein 0.49

STM4374 yjfL Putative inner membrane protein 0.07

STM4498 Putative inner membrane protein 0.06

STM4591 sthE Putative major fimbrial subunit 0.15

Cellular processes

STM0332 Putative hydrolase or acyltransferase 0.16

STM1087 pipA Pathogenicity island encoded protein: SPI3 0.18

STM1088 pipB Pathogenicity island encoded protein: SPI3 0.20

STM1233 ycfC Membrane associated protein of unknown function 0.19

STM1691 pspF Transcription activator 0.22

Cellular intermediary metabolism

STM0084 Putative sulfatase 0.46

STM0692 Putative transcriptional regulator, LysR family 0.49

STM1582 nhoA Putative arylamine N-acetyltransferase 0.34

STM2915 ygbM Putative endonuclese 0.15

DNA metabolism

STM0396 sbcD ATP-dependent dsDNA exonuclease 0.21

STM0451 hupB DNA-binding protein HU-beta, NS1 (HU-1) 0.36

STM1235 ymfB Putative MutT-like protein 0.20

STM3739 yicF Putative DNA ligase 0.45

Energy metabolism

STM0059 citD2 Putative citrate lyase acyl carrier protein (gamma chain) 0.37

STM0077 fixC Related to carnitine metabolism 0.38

STM0101 araD L-ribulose-5-phosphate 4-epimerase 0.45

STM1352 ydiS Flavoprotein 0.17

STM1468 fumA Fumarase A (fumarate hydratase class I), aerobic isozyme 0.18

STM2840 Putative flavoprotein 0.25

STM2976 fucI L-fucose isomerase 0.09b

STM3137 Putative uronate isomerase 0.10

STM3241 tdcE Pyruvate formate-lyase 4/ 2-ketobutyrate formate-lyase 0.37

STM4326 aspA Aspartate ammonia-lyase (aspartase) 0.11

STM4343 frdA Fumarate reductase, anaerobic, flavoprotein subunit 0.12

STM4432 Putative thiamine pyrophosphate-requiring enzyme 0.07

Mobile and extrachromosomal element functions

STM2776 iroE Putative hydrolase of the alpha/beta superfamily 0.13

Protein fate

STM0624 citC Citrate lyase synthetase (citrate (pro-3S)-lyase ligase) 0.22

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used as a marker for the production of clustered damage.

The composition of base damage and the degree of

clu-stering are quite different depending on clustered lesions,

and repair processes are likely to operate with different

rates and efficiencies. So, some of clustered damages may

be of trivial important while others may dominate the

radio-biological consequences. However, the identity of

cluster-ed lesions responsible for the biological effects of radiation

remains uncertain. Understanding the long-term effects of

ionizing radiation on living organisms requires

identifi-cation of critical radiation-induced DNA lesions,

measure-ment of their repairability, and determination of the

conse-quences of misrepaired or unrepaired persistent lesions.

In conclusion, the use of DNA arrays allowed us to

inve-stigate the pattern of changes in gene expression after a

relatively high dose (1 kGy) of gamma radiation. The

com-parison of our results with similar studies previously

publi-shed showed a discrepancy between the gene expression

patterns in response to the type of DNA damaging agents,

UV radiation, MMC, hydrogen peroxide, and gamma

radia-tion. This comparison presents one possibility that a high

dose of gamma radiation may generate the specific

SOS-inducing signal due to the nature ionizing radiation, which

can cause the clustered damage of DNA.

Table 2. Continued.

Proteins synthesis

STM1337 pheS Phenylalanine tRNA synthetase, alpha-subunit 0.17

STM1381 orf245 Putative cytoplasmic protein 0.36

STM4199 Putative cytoplasmic protein 0.12

Transport and binding proteins

STM0257 Putative drug efflux protein (perhaps for chloramphenicol) 0.16

STM0364 foxA Ferrioxaminereceptor 0.22

STM0382 Putative permease 0.20

STM0463 amtB Putative Amt family, ammonium transport protein 0.21

STM0498 ybaR Putative copper-transporting ATPase 0.22

STM0665 gltI ABC superfamily (binding_prot.), glutamate/aspartate transporter 0.29

STM0770 Putative ABC transport protein 0.41

STM1493 Putative periplasmic component, ABC transport system 0.16

STM1635 Putative ABC-type polar amino acid transport system 0.47

STM2421 xapB MFS superfamily, xanthosine permease 0.39

STM2558 cadB APC family, lysine/cadaverine transport protein 0.17

STM3243 tdcC HAAAP family, L-threonine/ L-serine permease 0.36

Unclassified

STM1241 msgA Macrophage survival gene; reduced mouse virulence 0.35

STM1384 ttrC Tetrathionate reductase complex, subunit C 0.32

STM2788 Tricarboxylic transport 0.43

STM3248 garR Tartronate semialdehyde reductase (TSAR) 0.44

STM3636 lpfE Long polar fimbrial minor protein 0.36

STM4308 Putative component of anaerobic dehydrogenases 0.11

Unknown function

STM0767 dcoA Pseudogene 0.26

STM1156 yceA Putative enzyme related to sulfurtransferases 0.20

STM1774 sirC Regulation of invasion genes 0.37

STM3119 Putative monoamine oxidase 0.09

STM3738 yigC Putative inner membrane protein 0.42

STM3776 yicM Putative MFS family tranport protein (1st mdule) 0.38

STM4078 yneB Putative fructose-1,6-bisphosphate aldolase 0.47

STM4539 Putative glucosamine-fructose-6-phosphate aminotransferase 0.16

a_{The ratio is the fold increase in mRNA level in irradiated culture compared to control culture.} b_{Ten genes whose expression is most highly altered by irradiation are indicated in bold.}

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ACKNOWLEDGEMENT

This study was supported by Ministry of Education,

Sci-ence and Technology (MEST), Korean government,

throu-gh its National Nuclear Technology Program.

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Manuscript Received: July 14, 2008 Revision Accepted: August 5, 2008