Abstract
In response to increased levels of Zn2+,SmtA, a metallothionein, is expressed in Synechococcus sp. PCC 7942, while ZiaA, a transporter of Zn2+,is expressed in Synechocystis sp. PCC 6803. Gene expressions for these proteins are regulated by repressor proteins, SmtB and ZiaR, respectively, both of which belong to ArsR family, but their levels of repression differ. To understand the different repression mechanism, we compared the cis-element in the promoter region of smtA and ziaA. The promoter region of smtA involved two inverted repeats and that of ziaA involved one similar repeat. Gel retardation assay revealed that SmtB formed four different complexes with the promoter region of smtA, whereas it formed two different complexes with that of ziaA. These results suggest that the formation of larger complexes of SmtB due to the two inverted repeats might repress the expression of smtA more tightly.
