A chlamydial plasmid is differentially transcribed during the life cycle of Chlamydia trachomatis

A 7.5-kb cryptic plasmid is found in all serotypes of the obligate intracellular parasite, Chlamydia trachomatis. Although at least nine open reading frames are apparent from sequence analysis of plasmid DNA, only a small region of approximately 500 bp has been consistently shown to be transcriptionally active by Northern blot analysis. In this study, transcription was analyzed using a host-free system in which RNA synthesized by chlamydiae isolated from host cells was hybridized to different regions of the plasmid. The results suggest that fragments corresponding to all open reading frames are transcribed, but at varied relative levels depending upon the stage of the life cycle. The hybridization patterns also suggested a net chemical degradation of plasmid-specified RNA in a 3' to 5' direction.