Evidence for involvement of pyrH+ of an Escherichia coli K-12 F-prime factor in inhibiting construction of hybrid merodiploids with Salmonella typhimurium.

Transconjugants were not recovered in matings between Salmonella typhimurium and Escherichia coli K-12 strains carrying the chromosomal region between leu and argF on an F-prime factor, even when a restriction-deficient recipient was used. A mutant F-prime factor compatible for transfer to S. typhimurium was constructed by transposon mutagenesis and characterized as being deficient in directing the synthesis of UMP kinase (encoded by pyrH). Other compatible F-prime factors were readily constructed by employing a procedure designed to select for strains carrying F-prime factors harboring pyrH mutations.