title: Construction of Zn2+/Cd(2+)-tolerant cyanobacteria with a modified metallothionein divergon: further analysis of the function and regulation of smt.
abstract: This paper reports the (de novo) construction of mutants of Synechococcus PCC 7942 lacking the repressor (SmtB) of the metallothionein gene, smtA. These smtA+/B- cells are more tolerant to elevated [Zn2+] and [Cd2+] than cells containing an intact metallothionein divergon (smt). Previously selected (by step-wise adaptation) Cd(2+)-tolerant mutants contain additional copies of smtA and possibly other undetected mutations. It is now confirmed that these cells also contain a deletion within 'all' copies of smtB and hence fail to revert to wild type following subculture in medium which has not been supplemented with Cd2+ or Zn2+. Northern analysis showed enhanced accumulation of smtA transcripts, even in the absence of added metal ions in these mutants. An increase in the accumulation of Zn2+ is reported in cells containing an intact metallothionein divergon compared to cells deficient in both smtA and smtB. This supports the assumption that SmtA binds Zn2+ within cyanobacterial cells. We also describe the use of the above mentioned mutants to identify additional factors involved in the regulation of transcription from the smtA operator-promoter.
authors.affiliation: Department of Biochemistry and Genetics, Medical School, University of Newcastle, UK.
authors.forename: J S
authors.initials: JS
authors.lastname: Turner
authors.forename: N J
authors.initials: NJ
authors.lastname: Robinson
authors.forename: A
authors.initials: A
authors.lastname: Gupta
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics; D001483:Base Sequence; D002104:Cadmium / Q000378:metabolism / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects; D000458:Cyanobacteria / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D005838:Genotype; D008668:Metallothionein / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015032:Zinc / Q000378:metabolism / Q000494:pharmacology*; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D012097:Repressor Proteins; C080048:smtA protein, Synechococcus; D002104:Cadmium; D008668:Metallothionein; D001616:beta-Galactosidase; D015032:Zinc