1a) and Southern blotting (not shown). Sequence analysis of five of these argR− mutants showed a five amino acid insertion (GVPLL) between the 149th selleck compound and the 150th residue of ArgR (Fig. 4). These mutations all mapped to the terminal α-6 helix of the protein, which we named ArgR5aa. An ArgR derivative

truncated at position 150 was constructed by site-directed mutagenesis. This truncated protein, called ArgR149, was tested for the ability to resolve pCS210 in the argR− strain (DS956/pCS210). ArgR149 displayed the same properties as ArgR5aa, the protein containing the GVPLL insertion between the 149th and the 150th residue, namely a significant reduction in cer site-specific recombination in vivo (Fig. 1b) and the ability to repress an argA∷lacZ fusion in vivo. In order to quantify the levels of repression of the argA∷lacZ fusion in EC146(λAZ-7) with both wild-type and mutant ArgRs, β-galactosidase assays were performed. EC146(λAZ-7) does not produce a functional ArgR, and as a result, expresses β-galactosidase constitutively from the argA∷lacZ promoter fusion (128.15 Miller units). In the presence of a wild-type argR gene (present in a pUC19 plasmid), the levels of this enzyme were

reduced 25-fold (3.5 Miller units). A cloned ArgR mutant containing the C-terminal pentapeptide insertion (ArgR5aa) repressed the fusion sevenfold (19 Miller units), and the clone containing the truncated ArgR (ArgR149) repressed 33-fold (5.4 Miller Units) (Fig. 2). The variant ArgR proteins (ArgR5aa and Dabrafenib ArgR149) were then analysed for specific binding to ARG box sites using gel-mobility shift assays. The mutant proteins all retarded the migration of a digoxygenin-labelled E. coli ARG box (Fig. 3). Lanes 2–6 and 9–13 show the effect of the increasing

Liothyronine Sodium concentrations of mutant proteins on their binding activity in the presence of a constant quantity of poly-dIdC and digoxygenin-labelled DNA. A retarded complex was observed at low protein concentrations, which became more apparent as the protein concentration increased. The retarded complexes obtained with the mutant proteins displayed a slightly slower migration than that observed with wild-type ArgR–DNA complexes (Fig. 3, lanes 7 and 14). A labelled nonspecific DNA fragment was not retarded in its migration in the presence of wild-type or mutant ArgR proteins (data not shown). The wild-type and mutant forms of ArgR were then subjected to crosslinking analysis (Fig. 5) using glutaraldehyde. All forms of the protein were able to form higher-order multimeric complexes. Both wild-type ArgR and ArgR5aa form hexamers in the presence of 0.08% glutaraldehyde (Fig. 5, lanes 4 and 8).