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Characterization of late gene promoters of Chlamydia trachomatis

Chlamydiae possess an intracellular developmental cycle defined by the orderly interconversion of infectious, metabolically inactive elementary bodies and noninfectious, dividing reticulate bodies. Only a few stage-specific genes have been cloned and sequenced, including the late-stage cysteine-rich protein operon and two late-stage genes encoding histone-like proteins. The aims of this study were to identify additional late-stage genes of Chlamydia trachomatis, analyze the upstream DNA sequence of late genes, and determine the sigma factor requirement of late genes. Stage-specific RNA, made by chlamydiae isolated from host cells, was used to probe C. trachomatis genomic libraries. Two new late genes, designated ltuA and ltuB, were identified, cloned, and sequenced. The predicted peptides encoded by ltuA and ltuB do not bear strong homology to known proteins, and the function of the new late genes is not known. The 5' ends of the transcripts of ltuA, ltuB, the cysteine-rich protein operon, and the two histone-like genes (hctA and hctB) were mapped, and a consensus -10 promoter region of TATAAT was derived from their upstream DNA sequences. In vitro transcription from templates encoding the promoter regions of ltuA, ltuB, and hctA cloned into the transcription assay vector pUC19-spf was found to be strongly stimulated by the addition of recombinant chlamydial sigma 66, while transcription from the putative hctB promoter region cloned in pUC19-spf was not detected in either the presence or absence of added sigma 66. These results suggest that the transcription of at least some chlamydial late-stage genes is dependent on sigma 66, which is homologous to the major sigma factors of other eubacteria.