Morita E H, Wakamatsu M, Hayashi H
Center for Gene Research, Ehime University, 3-5-7 Tarumi, Matsuyama, Ehime 790-8566, Japan.
Nucleic Acids Res Suppl. 2001(1):251-2. doi: 10.1093/nass/1.1.251.
Tolerance to the heavy-metal ion stress in cyanobacterial cell is regulated by the transcriptional repressor SmtB that senses the Zn/Cd concentration in the cell. SmtB regulated the transcriptional level of class II metallothionein, SmtA. There are two recognition DNA sequences (Bbs1 and Bbs2) in the operator/promoter region of smtA gene. To clear the functional meaning of the presence of these two sequences, we have compared the affinities of native and point-mutated SmtBs to these two sites. We also have compared the sizes of the protein-DNA complexes being formed with these two sites. SmtB forms protein-DNA complex in an unique size with Bbs1, in three different sizes with Bbs2. We have further designed the modified Bbs1 and Bbs2 sequences, and the results obtained with these sequences indicate that the differences observed between the cases of Bbs1 and Bbs2 are caused by the presence of direct repeat sequence and the differences in the linker sequences.
