Differential expression of the psbA genes in the cyanobacterium Synechocystis 6803.
The 5' region and transcription initiation sites of the psbA-2 and psbA-3 genes of Synechocystis 6803 were determined. The otherwise highly homologous genes were shown to diverge significantly in the 5' noncoding regions. The transcription start site for the psbA-2 gene was mapped to position -49 upstream of the coding region and for the psbA-3 gene to position -88, i.e. 38 bp upstream of the psbA-2 transcription start point. Both genes exhibit promoter elements, which conform in sequence and position to Escherichia coli consensus motifs. The two genes share identical -35 sequences but differ in their -10 sequences. Primer extension analysis demonstrated that the psbA-2 and psbA-3 genes are differentially expressed, with > 90% of the total psbA transcripts being produced by the psbA-2 gene and the rest by the psbA-3 gene. Inactivation of the psbA-2 gene resulted in an eightfold up-regulation of the psbA-3 gene. The strikingly higher stability of the psbA transcripts in darkness compared to light, and the accumulation of a specific decay intermediate under dark conditions was reported previously. We show here that this dark-stability applies to both the psbA-2 and psbA-3 transcripts. The psbA-3 transcript did not appear to produce the processed intermediate, arguing for the involvement of the 5' non-coding region as a determinant in psbA transcript degradation.
Mohamed
A
A
Department of Biochemistry, Arrhenius Laboratories, University of Stockholm, Sweden.
Eriksson
J
J
Osiewacz
H D
HD
Jansson
C
C
D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D000458:Cyanobacteria / Q000235:genetics*; D004269:DNA, Bacterial / Q000235:genetics / Q000302:isolation & purification; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides; D045332:Photosystem II Protein Complex; D010940:Plant Proteins / Q000235:genetics*; D011401:Promoter Regions, Genetic; D012689:Sequence Homology, Nucleic Acid; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D009838:Oligodeoxyribonucleotides; D045332:Photosystem II Protein Complex; D010940:Plant Proteins