Synthetic multifunctional proteins

Summary Several E. coli mutants were isolated which produce triple chimeras between one of the trp enzymes lac, repressor and -galactosidase. The mutants were isolated as TonB^- Lac⁺ derivatives of a phenotypically Lac^- TrpR^- strain carrying a lac I⁺-Z⁺ fusion on a 80dlac phage. The phage is integrated into the chromosome in such a way that the lac and the trp genes are transcribed in the same direction. Of a total of 58 candidates 2 TrpA^- and 3 Trp^- strains produce triple chimeras. The chimeras from the two TrpA^- strains were further examined. They consist of tryptophan synthetase -subunit, lac repressor and -galactosidase. In crude extracts of these strains the tryptophan synthetase -subunit part can be identified by its ability to aggregate with the -subunit since some of the -subunit activity can be precipitated with antiserum against -galactosidase. Furthermore -galactosidase precipitates with antiserum against tryptophan synthetase -subunit. The lac repressor part is able to bind IPTG, but not lac operator DNA in vitro. The -galactosidase part is as unaffected as in the original lac repressor--galactosidase chimera. The molecular weigths of both chimeras are 175,000 when determined by SDS gel electrophoresis. The chimeras are partially degraded giving rise to fragments of distinct molecular weights.