Regulation of tryptophan synthase gene expression in Chlamydia trachomatis.
We previously reported that Chlamydia trachomatis expresses the genes encoding tryptophan synthase (trpA and trpB). The results presented here indicate that C. trachomatis also expresses the tryptophan repressor gene (trpR). The complement of genes regulated by tryptophan levels in C. trachomatis is limited to trpBA and trpR. trp gene expression was repressed if chlamydiae-infected HeLa cells were cultured the presence of tryptophan and induced if grown in tryptophan-depleted medium or in the presence of IFN-gamma. Furthermore, expression of the trp genes in strains which encode a functional tryptophan synthase is repressed when infected cells are cultured in the presence of the tryptophan precursor indole. Results from experiments with cycloheximide, an inhibitor of eukaryotic protein synthesis, indicate that in addition to the absolute size of the intracellular tryptophan pool, host competition for available tryptophan plays a key role in regulating expression of the trp genes. The tryptophan analogue, 5-fluorotryptophan, repressed trp gene expression and induced the formation of aberrant organisms of C. trachomatis. The growth-inhibitory properties of 5-fluorotryptophan could be reversed with exogenous tryptophan but not indole. In total, our results indicate that the ability to regulate trp gene expression in response to tryptophan availability is advantageous for the intracellular survival of this organism. Furthermore, the fact that C. trachomatis has retained the capacity to respond to tryptophan limitation supports the view that the in vivo antichlamydial effect of IFN-gamma is via the induction of the tryptophan-degrading enzyme, indoleamine 2,3-dioxygenase.
Wood
Heidi
H
National Microbiology Laboratory, Health Canada, 1015 Arlington Street, Winnipeg, Manitoba, Canada R3T 2N2.
Fehlner-Gardner
Christine
C
Berry
Jody
J
Fischer
Elizabeth
E
Graham
Bonnie
B
Hackstadt
Ted
T
Roshick
Christine
C
McClarty
Grant
G
D001426:Bacterial Proteins; D002692:Chlamydia trachomatis / Q000235:genetics* / Q000254:growth & development; D003513:Cycloheximide / Q000494:pharmacology; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D005809:Genes, Regulator; D006367:HeLa Cells; D006801:Humans; D002479:Inclusion Bodies / Q000382:microbiology; D007211:Indoles / Q000378:metabolism / Q000494:pharmacology; D007371:Interferon-gamma / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000096:biosynthesis; D012097:Repressor Proteins / Q000235:genetics / Q000502:physiology; D014158:Transcription, Genetic; D014364:Tryptophan / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D014366:Tryptophan Oxygenase / Q000096:biosynthesis; D014367:Tryptophan Synthase / Q000096:biosynthesis / Q000235:genetics*; D029968:Escherichia coli Proteins
D001426:Bacterial Proteins; D003513:Cycloheximide; D007211:Indoles; D007371:Interferon-gamma; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D012097:Repressor Proteins; D014364:Tryptophan; D014366:Tryptophan Oxygenase; D014367:Tryptophan Synthase; C027190:TRPR protein, E coli; D029968:Escherichia coli Proteins; C026927:5-fluorotryptophan; C095066:5-fluoroindole; C030374:indole