Cloning of genes that suppress an Escherichia coli K-12 alanine auxotroph when present in multicopy plasmids.

To facilitate molecular analyses of a previously uncharacterized gene involved in alanine synthesis, attempts were made to clone the wild-type allele of this gene, alaA, with a mini-Mu plasmid element used for in vivo cloning. Seventy-six independent Ala+ plasmids were isolated and characterized. Physiological, enzymological, and restriction endonuclease analyses indicated that three different genes, none of them alaA, were cloned. These genes were avtA+, which encodes the alanine-valine transaminase (transaminase C); tyrB+, which encodes the tyrosine-repressible transaminase (transaminase D); and a previously undescribed gene, called alaB, which encodes an alanine-glutamate transaminase.     

Genetic mapping of a mutation conferring sensitivity to bacteriophage Mu in Salmonella typhimurium LT2.

Two strains of Salmonella typhimurium LT2, SA1475 and MA411, were fortuitously found to be sensitive to bacteriophage Mu. The Mu-sensitivity allele of SA1475 was called musA1 and shown to be linked to the histidine operon both in conjugation and transduction experiments. The Mus allele of MA411 was unlinked to the his region and was tentatively designated musB2. Strains carrying large deletions of the his operon were also tested for Mu sensitivity; those of which the his-rib region is deleted were also sensitive to Mu. Transduction data led to the order zee-2 hisOGDCBAHFIE gnd musA. An Hfr injecting the his operon early (HfrK9) an carrying hisG9424::Tn10 delta 4 delta 11 and musA1 was isolated; this Hfr made it possible to introduce the Mus character into most derivatives of S. typhimurium LT2. Since strain SA1475 is resistant to bacteriophage P1, it could be used to select a new P1-Mu hybrid which has the host range of Mu and the transduction properties of P1.