Synthetic multifunctional proteins

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Abstract
Several E. coli mutants were isolated which produce triple chimeras between one of the trp enzymes lac, repressor and β-galactosidase. The mutants were isolated as TonB- Lac+ derivatives of a phenotypically Lac- TrpR- strain carrying a lac I+-Z+ fusion on a ϕ80dlac 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 α-subunit, lac repressor and β-galactosidase. In crude extracts of these strains the tryptophan synthetase α-subunit part can be identified by its ability to aggregate with the β-subunit since some of the β-subunit activity can be precipitated with antiserum against β-galactosidase. Furthermore β-galactosidase precipitates with antiserum against tryptophan synthetase α-subunit. The lac repressor part is able to bind IPTG, but not lac operator DNA in vitro. The β-galactosidase part is as unaffected as in the original lac repressor-β-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.