Ch. Johnson et Gw. Schmidt, THE PSBB GENE-CLUSTER OF THE CHLAMYDOMONAS-REINHARDTII CHLOROPLAST - SEQUENCE AND TRANSCRIPTIONAL ANALYSES OF PSBN AND PSBH, Plant molecular biology, 22(4), 1993, pp. 645-658
We have sequenced and characterized the complete psbB gene cluster of
Chlamydomonas reinhardtii chloroplast DNA. Although the petB and petD
genes are located elsewhere, the sequential order of psbB, ORF31, psbN
and psbH is identical to that of the psbB operon in higher plants. Al
so, intergenic non-coding regions are much larger in the Chlamydomonas
gene cluster. Northern blot analyses indicate the formation of dicist
ronic transcripts of psbB and ORF31 and monocistronic transcripts of p
sbN and psbH. It is unclear whether a psbB operon is transcribed to yi
eld a large polycistronic precursor but northern blot analysis with to
tal RNA from cells grown at 15-degrees-C does not detect an increased
complexity of the transcripts, as has been found in studies of the psb
B operon of higher plants. From primer extension and nuclease protecti
on assays, it is apparent that 5' and 3' processing of the primary psb
H transcript results in the accumulation of a heterogenous population
of mRNAs. Northern blot analyses reveal transcription of Chlamydomonas
psbN and show that its mRNA is much larger than that identified in li
verwort and pea. The sequence identities of the PSII-H and PSII-N poly
peptides as compared to their vascular plant counterparts is 50 to 62%
. While the amino acid sequences of PSII-H and PSII-N proteins are sig
nificantly conserved, the mass of PSII-H from Chlamydomonas is signifi
cantly larger.