Intra-cistronic complementation among trpC mutants of Escherichia coli

Summary Some merodiploids containing two different trpC alleles grow in the absence of added tryptophan. The trpC gene product is the bifunctional enzyme indoleglycerol phosphate synthetase but the ability to grow on minimal medium does not require that the alleles be dificient in different functions. This indication of complementation is supported by the evidence that the trpC alleles, of the merodiploids, can be transferred by transduction or by the trp-colV,B episome. Genetic recombination between episome and chromosome is seen to occur, but at a rate too low to explain the observed results. The nature of the interaction between the trpC alleles is not readily explained since indoleglycerol phosphate synthetase appears to consist of a single polypeptide chain in in vitro studies.