Transcript analysis of the pcbABC genes encoding the antenna apoproteins in the photosynthetic prokaryote,...

The tightly linked pcbABC genes encode the chlorophyll a/b-binding apoproteins in the oxygenic photosynthetic prokaryote Prochlorothrix hollandica. Northern blotting experiments employing gene-specific DNA probes have identified a complex pattern of transcription from the pcb region. A large 4.4-kb transcript detected in cultures maintained in high light, low light and in darkness results from the cotranscription of all three genes, whereas pcbAB, pcbBC and individual pcbA, B, and C mRNAs are similarly detected in all light regimes. The half lives of the RNAs vary from 15 min for the pcbABC transcript, to over 60 min for the pcbA and pcbC mRNAs. The lack of identifiable promoter sequences other than the region upstream from pcbA, plus the enhanced stability of the individual single gene transcripts, suggest that the smaller RNA species arise from processing of larger transcripts. Transcription and mRNA turnover occurs largely independent of light intensity, in contrast to what is seen in most other phototrophs, in which light influences the accumulation of antenna apoprotein gene mRNAs.