The transcriptional repressor EUO regulates both subsets of Chlamydia late genes

Abstract

The pathogenic bacterium Chlamydia replicates in a eukaryotic host cell via a developmental cycle marked by temporal waves of gene expression. We have previously shown that late genes transcribed by the major chlamydial RNA polymerase, σ66 RNA polymerase, are regulated by a transcriptional repressor EUO. We now report that EUO also represses promoters for a second subset of late genes that are transcribed by an alternative polymerase called σ28 RNA polymerase. EUO bound in the vicinity of six σ28-dependent promoters and inhibited transcription of each promoter. We used a mutational analysis to demonstrate that the EUO binding site functions as an operator that is necessary and sufficient for EUO-mediated repression of σ28-dependent transcription. We also verified specific binding of EUO to σ66-dependent and σ28-dependent promoters with a DNA immunoprecipitation assay. These findings support a model in which EUO represses expression of both σ66-dependent and σ28-dependent late genes. We thus propose that EUO is the master regulator of late gene expression in the chlamydial developmental cycle.