Part:BBa_K3470001

RBS (B0034) + MerR (Mercury-responsive transcription factor)

The regulation of mer operon expression in gram-negative bacteria has been extensively studied. MerR protein also regulates its own synthesis from the PmerR promoter, which is divergently oriented from PmerT. A 7-bp dyad sequence is located within the -10 and -35 sequences of PmerT. The -10 and -35 sequences for PmerT are separated by 19 bp, 2 bp more than the optimal spacing for efficient transcription by the Escherichia coli a70 RNA polymerase. The 19-bp spacing, dyad sequences, and relative position of the dyad sequence with respect to the -10 and -35 sequences are important for induction and repression of the operon. Spacer deletion mutations outside the MerR binding sequence increased constitutive promoter activity, which was repressed by MerR even in the presence of Hg(II) salts. The three cysteine residues are conserved in all MerR proteins. These were originally suggested as the site of Hg(II) binding, and this was confirmed by a variety of methods including mutagenesis of the cysteines to alanine or serine in which the Hg(II)-dependent activation is lost and spectroscopy showing S-Hg(II) bonding. The MerR protein, which was identified by sequence similarity searches, was overexpressed in E. coli. The Bacillus MerR positively regulated transcription of the Bacillus mer operon, but not the TnSO1 mer operon, in the presence of Hg2+. Sequence analysis of different MerR proteins and the promoters on which they act, suggest that information from the Gram-negative systems and the Gram-positive MerR activators applies to each of the other systems. An exception is the MerR repressor of S.lividans which is a member of the SmtB/ArsR regulator family. merR encodes a trans-acting repressor/activator protein (NiBhriain et al., 1983) and is separated from the other mer genes by a short sequence of a cis-acting operator-promoter element. The merR gene is transcribed divergently from the other mer genes that are co-transcribed as a single polycistronic mRNA. A study performed using the beta-lactamase assay indicated that the mer promoter functions very poorly in the absence of merR and its activity is not detectable by the beta-lactamase assay used. They concluded that the product of the merR gene is a trans-acting factor that activates transcription of the mer operon in the presence of specific inducer Hg2+ (or Cd2+) (Chu et al., 1992)

Sequence and Features

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  COMPATIBLE WITH RFC[12]
• 21
  COMPATIBLE WITH RFC[21]
• 23
  COMPATIBLE WITH RFC[23]
• 25
  COMPATIBLE WITH RFC[25]
• 1000
  COMPATIBLE WITH RFC[1000]