Cotranscription of the genes encoding two P700 chlorophyll a apoproteins with the gene for ribosomal protein CS14: determination of the transcriptional initiation site by in vitro capping.

Transcription of the psaA operon in tobacco chloroplasts has been studied. This operon contains in linear sequence the genes encoding the P700 chlorophyll a A1 and A2 apoproteins (psaA and psaB) and the gene encoding the ribosomal CS14 protein (rps14). Northern blot hybridization revealed that a 5.2 kb transcript hybridizes to psaA, psaB, and rps14, but not to the fMet-tRNA (trnfM) gene which follows. Primer extension and in vitro capping assays indicated that the transcriptional initiation site is 194 bp upstream of psaA. The 3' end of the transcript was determined by S1 mapping to be 105 bp downstream of rps14. The transcript is calculated to be 5,207 nucleotides long.