Mohamed A, Eriksson J, Osiewacz H D, Jansson C
Department of Biochemistry, Arrhenius Laboratories, University of Stockholm, Sweden.
Mol Gen Genet. 1993 Apr;238(1-2):161-8. doi: 10.1007/BF00279543.
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.
确定了集胞藻6803的psbA - 2和psbA - 3基因的5'区域和转录起始位点。结果表明，这两个原本高度同源的基因在5'非编码区存在显著差异。psbA - 2基因的转录起始位点定位于编码区上游- 49位，psbA - 3基因的转录起始位点定位于- 88位，即比psbA - 2转录起始点上游38 bp处。两个基因均表现出启动子元件，其序列和位置符合大肠杆菌共有基序。这两个基因共享相同的- 35序列，但- 10序列不同。引物延伸分析表明，psbA - 2和psbA - 3基因存在差异表达，psbA转录本总量的> 90%由psbA - 2基因产生，其余由psbA - 3基因产生。psbA - 2基因的失活导致psbA - 3基因上调8倍。先前报道了与光照相比，黑暗中psbA转录本具有显著更高的稳定性，以及在黑暗条件下一种特定降解中间体的积累。我们在此表明，这种黑暗稳定性适用于psbA - 2和psbA - 3转录本。psbA - 3转录本似乎不会产生加工中间体，这表明5'非编码区参与了psbA转录本的降解过程。
