Abstract

Zinc is an abundant transition metal in the biosphere. Because of its Lewis acidity, flexible cordination geometry, rapid ligand exchange property and absence of redox activity, Zn is used as a metal of choice in many biological reactions. In addition, Zn-binding Zn finger protein form an important class of DNA-binding transcriptional regulators. A number of Zn transporter systems have been identified in yeast, human and plants. An ABC-type Zn-permease and a Zn-binding repressor protein have been identified in E. coli. The complete genome sequence of Synechocystis PCC 6803 revealed that the slr2043-slr2044-slr2045 cluster of ORFs are homologous to the mntCAB (encoding a Mn-permease). Inactivation of each of these ORFs in this study resulted in mutant strains that grow poorly in the absence of added Zn in the growth medium. Analysis of these mutant strains has established that this operon encodes a Zn-uptake transporter. Zn is toxic to the cells and Synechocystis possesses Zn exporter encoded by slr0798 to keep the intracellular Zn concentration at low level. DNA microarray analysis revealed that the expression of many genes is up-regulated or down-regulated in response to the increase of external Zn concentration. We shall enlist these genes.

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