Thymine at 5 Is Crucial for cpc Promoter Activity of

The levels of transcripts of the cpc operon were highly reduced in a PD-1 mutant of cyanobacterium Synechocystis sp. strain PCC 6714. This was due to a substitution of C for T that occurred at 5 bp upstream of the transcription initiation site of the cpc operon. Any substitution for T at the 5 position drastically reduced both in vivo and in vitro promoter activity in cyanobacterium Synechococcus sp. strain PCC 7942 but not the in vivo activity in Escherichia coli. This suggests that the requirement of 5T appears to be specific for a cyanobacterial RNA polymerase-promoter combination. Cyanobacteria are photosynthetic prokaryotes that are con-sidered to be the ancestors of chloroplasts. Cyanobacteria have been investigated intensively, as a model of oxygen-evolving photosynthetic organisms, in various aspects such as photosyn-thesis and gene expression. We have found that a single base substitution has occurred in the cpc operon in a phycocyanin-deficient mutant of the cyanobacterium Synechocystis sp. strain PCC 6714, PD-1 (13). The cpc operon comprises cpcBAC1C2D, which encodes phy