Source:
Generated By: https://synbiohub.org/public/igem/igem2sbol/1
Created by: Tong Li
Date created: 2014-09-25 11:00:00
Date modified: 2015-07-23 03:26:04
Coding for the trans-acting regulator SmtB
| Types | DnaRegion |
| Roles | CDS Coding |
| Sequences | BBa_K1509000_sequence (Version 1) |
Description
In 1993, Huckle and co-workers reported the isolation and analysis of the smt locus from Synechococcus sp.. Gene smtB, one of the components of the locus, encodes a transcriptional repressor of gene smtA, with which is required for normal tolerance to Zn2+ and Cd2+. The product of smtB functions by binding to the smt operator-promoter(smtO-P) and dissociating in the presence of Zn2+ due to the classical helix-turn-helix motif similar to many DNA-binding proteins. It can also be genomically rearranged when induced by Cd2+, leading to a deletion within smtB because of a highly iterated palindrome (HIP1), a highly represented octanucleotides(5′-GCGATC-GC-3′) which traverse both borders of the excised element. These two mechanisms both cause the elevated expression of smtA.Notes
According to the mechanisms of smt locus represented above, gene smtB should function with the accompany of smt operator-promoter. Previous cases selected smtA whose product functions by encoding MT-like to sequester metal ions, while our case intended to take advantage of the trigger lies in this locus. By imitating former researches, in which a promoter less lacZ gene was fused upstream of smtA, we respectively splice two selected reporter genes and sequence from smt operator-promoter to smtB, equivalent to replacing smtA with reporter genes, to visualize the effects of metal ions on the locus.Source
Metallothioneins(MTs), discovered in horse kidney in 1957 by Margoshes and Vallee are identified as low-molecular weight and sulphydryl rich proteins which bind metal ions in metal-thiolate clusters and whose synthesis increases in response to elevated concentrations of certain metals.In 1988, Olafson and co-workers reported the amino acid sequence of a metal-associated protein isolated from cyanobacterium Synechococcus sp.. With the function of binding metal ions remaining, it only has less than 20% homology in amino acid sequence with known MTs in eukaryotes and thus we call it class II MT or on some occasions MT-like.
Owing to the works of Robinson and Huckle, the corresponding locus of Synechococcus PCC7942, smt locus was isolated and analyzed. It includes smtA which encodes the class II MT and a divergently transcribed gene smtB which encodes a trans-acting, autoregulatory repressor that exerts metal ion-inducible negative control over smtA transcription. Between them lies a 100-bp operator-promoter region(smt O-P, BBa_K1509001), which is responsible for the divergent orientation of smtA and smtB.