Detection of multiple, unspliced precursor mRNA transcripts for the Mr 32,000 thylakoid membrane protein from Euglena gracilis chloroplasts.

The psbA gene is the coding locus for a polypeptide of 32 kilodaltons that is involved in electron transport through photosystem II. The 4.9 kilobasepair (kbp) EcoRI restriction endonuclease fragment EcoI from the 145 kbp Euglena gracilis chloroplast DNA was shown to encode psbA. Five transcripts of size 3.1, 2.8, 2.3, 1.8, and 1.2 kilobases were detected by hybridization of psbA probes to nitrocellulose filter blots of electrophoretically separated RNAs. This same pattern was observed when the hybridization probe consisted of only exon sequences from this split gene. A synthetic, intron specific probe hybridized to all RNA precursors except the 1.2 kb mature RNA. These results and psbA DNA sequence data lead to the conclusion that the four higher molecular weight transcripts are unprocessed precursors of the 1.2 kilobase RNA, some of which contain unspliced intervening sequences. There is an increase in psbA transcripts during light induced maturation of the chloroplasts.