A Carboxyl-terminal Cys2/His2-type Zinc-finger Motif in DNA Primase Influences DNA Content inSynechococcus PCC 7942

Abstract

The DNA primase gene, dnaG, has been isolated from the cyanobacterium Synechococcus PCC 7942. It is not part of a macromolecular synthesis operon but is cotranscribed with pheT and located adjacent to the metallothionein divergon, smt. caused an increase in intensity, and a reduction in wavelength, of Trp fluorescence at the tip of the predicted zinc-finger, while EDTA caused the converse. Cells containing a single chromosomal codon substitution (C597S), altering the zinc-finger, were generated by exploiting Zn 2؉ -sensitive smt mutants and the proximity of dnaG to smt. Cells in which smt and dnaG(C597S) had integrated into the chromosome were selected via restored Zn 2؉ tolerance. Synechococcus PCC 7942 and its dnaG(C597S) mutant grew at equivalent rates, but the latter had a reduced number of chromosomes.

Coordination of Zn2+ (and Cd2+) by Prokaryotic Metallothionein

“…There is evidence to support a role for mammalian MT in the donation of Zn 2ϩ to Zn 2ϩ -binding proteins (25)(26)(27)(28)(29)(30). It has been hypothesized that SmtA may donate Zn 2ϩ to DNA primase (DnaG), which in Synechococcus PCC 7942 contains two Zn 2ϩ binding sites and is encoded by a gene that is located next to the smtA gene (31). Similarities between metal binding domains provided a clue to the existence of interaction between a copper chaperone and its receptor (32).…”

A metallothionein containing a zinc finger within a four-metal cluster protects a bacterium from zinc toxicity

“…8, which is published as supplemental data; A.K.R., M.D.H., C.A.B., J.A.P., P. Bowness, P.J.S., and N.J.R., manuscript in preparation). Zinc fingers were thought to be confined to eukaryotes, but recent studies have indicated the presence of Krüppel-like zinc fingers in some prokaryotes (5,(44)(45)(46), although they remain to be confirmed by structure determination.…”

“…Mutants lacking the smtA locus are hypersensitive to elevated zinc (5-fold), but otherwise viable (4). In addition to sequestering excess, it has been postulated that SmtA may be involved in controlling the intracellular distribution of zinc (5), but a specific partner (protein or DNA) for interaction with SmtA has not yet been identified.…”

“…Mammalian isoforms MT-1 and -2 are commonly isolated with seven Zn 2ϩ ions bound exclusively to the thiolate groups of cysteine residues in two clusters (8). In view of the cellular importance of zinc, there is considerable interest in establishing the conditions in which, and locations where, MT acquires or releases zinc (5,(9)(10)(11)(12)(13).…”

Cobalt-dependent Transcriptional Switching by a Dual-effector MerR-like Protein Regulates a Cobalt-exporting Variant CPx-type ATPase

“…The genotype of transformants was checked by PCR using primers 3 and 5Ј-GATTAACCGTTGACCAGCGCTAG-3Ј, which anneal to cbiE sequences flanking the site of cat insertion. The detected products revealed transformants to be merodiploid, with some chromosomes retaining cbiE and others containing cat within cbiE, with analogy to previous attempts to disrupt an essential cyanobacterial gene (24).…”