σ28 RNA polymerase regulates hctB, a late developmental gene in Chlamydia

Summary

Chlamydia is predicted to encode two alternative sigma factors that could provide a mechanism for the regulation of gene expression via alternative forms of RNA polymerase. We have demonstrated that σ²⁸, one of these alternative sigma factors, is transcriptionally active. Chlamydial σ²⁸ RNA polymerase was reconstituted from recombinant σ²⁸ protein and core enzyme that was biochemically isolated from chlamydiae. In an in vitro transcription assay, σ²⁸ RNA polymerase transcribed the hctB promoter in a σ²⁸-dependent manner. Transcription by σ²⁸ RNA polymerase was salt tolerant compared with transcription by σ⁶⁶ RNA polymerase, the major form of chlamydial RNA polymerase. As hctB encodes a histone-like protein that is only expressed late in the developmental cycle, our results suggest that σ²⁸ RNA polymerase has a role in the regulation of late gene expression in Chlamydia.