IDENTIFICATION OF A NOVEL TRANSCRIPTION REGULATOR FROM PROTEUS-MIRABILIS, PMTR, REVEALED A POSSIBLE ROLE OF YJAI PROTEIN IN BALANCING ZINC IN ESCHERICHIA-COLI

Zinc is an essential trace element required for structural integrity a nd functional activity of numerous proteins, yet mechanisms by which c ells regulate zinc concentration are poorly understood. Here, we ident ified a gene from Proteus mirabilis that encodes a 135-amino acid resi due protein, PMTR (P. mirabilis transcription regulator), a new member of the MerR family of transcription activators. Transformation of Esc herichia coli with PMTR-carrying vectors specifically increases cell t olerance to zinc, suggesting the role of PMTR in zinc homeostasis. In response to zinc, PMTR-containing cells robustly accumulate a 12-kDa p rotein, the amount of which correlates with the cells' ability to grow at high zinc concentrations. The 12-kDa protein is not induced in the presence of Ni2+, Co2+, Cd2+, Mn2+, or Fe2+, indicating that the PMTR -dependent expression of the 12-kDa protein is specifically regulated by zinc. The 12-kDa protein was identified as the C-terminal fragment off. coli protein YJAI, and was shown to contain two zinc-binding moti fs, Metal-affinity chromatography and Zn-65 blotting assay confirmed t he ability of the 12-kDa protein to bind zinc specifically (zinc > cob alt much greater than cadmium). We propose that YJAI is an important c omponent of the zinc-balancing mechanism in E. coli, the up-regulation of which with PMTR results in an increased tolerance to zinc.