Difference between revisions of "Part:BBa K566008"

Latest revision as of 18:42, 28 September 2011

Mnt repressor optimized for E. coli

Mnt repressor optimized from part BBa_C0072 with preferential codon usage for improved expression in E. coli. It negatively regulates Mnt repressible promoter (BBa_R0073).

Usage and Biology

Mnt protein contains 82 amino acid residues and forms a tetramer in solution. It is encoded by the immI (Immunity) region of Salmonella phage P22, involved in the maintenance of lysogeny or the commitment to lytic growth. The immI region also codes for the Ant protein and the Arc repressor. Ant induces lytic growth of the prophage. During lysogenic growth, Mnt represses Ant, maintaining the lysogen state. Rightward transcription of the arc and ant genes initiates at Pant and can be negatively regulated by either Mnt or Arc. Transcription of mnt initiates at Pmnt and proceeds to the left. The Pant and Pmnt promoters overlap physically and compete for RNA polymerase. The Mnt operator site overlaps the -35 region of Pmnt and the startpoint of Pant transcription (Figure 1).

Figure 1. Immunity region of P22. In the boxes, the -35 and -10 regions of Pant and Pmnt. Source: Vershon KA et al. (1987) J Mol Biol 195:311-322

Figure 2 shows the effect of Mnt concentration on run-off transcripts initiated at these two promoters. As the Mnt concentration is raised, transcription from Pant is repressed, whereas transcription from Pmnt, is stimulated. The stimulation of Pmnt transcription by Mnt corresponds to an approximate sixfold increase over basal transcription. In the absence of Mnt protein, the Pant promoter is much stronger than the Pmnt promoter.

Figure 2. Immunity region of P22. Amount of transcript produced in vitro as a function of different concentrations of Mnt. Circles represent the number of run-off transcripts from Pant. Triangles represent the number of run-off transcripts from Pmnt. Figure taken from Vershon KA et al. (1987) J Mol Biol 195:311-322

Sequence and Features