Histidine-Requiring Mutants of Escherichia Coli K12

I N Salmonella typhimurium a cluster of nine genes controlling histidine biosynthesis has been mapped in detail and correlated with enzymes in the biochemical pathway.Numerous observations are in accord with the concept of a unified control-or operon system-for the histidine genes in Salmonella (LOPER et al. 1964; AMES et al. 1967).Mutations leading to a requirement for histidine are known in Escherchia coli and have been located on the E. coli K12 genetic map (TAYLOR and TROTTER 1967) in a position comparable to that of the histidine operon in S. typhimurium (SANDERSON 1967).Data presented here indicate that the his genes in E. coli are clustered and may constitute an operon very similar to that of Salmonella.The 1 1 1 1 1 2 2 2 2 2 3 4 Ir ll ll h 4 3 aObtained through the courtesy of: (1) Dr. A. L. TAYLOR, (2) Dr. E. A. ADELBERG, (3) Drs.b F+ donors.c Hfr donors with F-attachment site 0-12, the same site as for AB312 (TAYLOR and ADELBERC d Strain description in Table 1 of GOLDSCHMIDT et al. (1970).T. S. MATNEY and E. GOLDSCHMIDT, (4) Isolated in this laboratory. 1960).were crossed in such plate matings with one another and with 190 Fhistidine auxotrophs.In similar tests, Salmonella strains carrying extended deletions in the his operon and F his episomes of E .coli origin (Table 2) were crossed with various Salmonella and E. coli mutants.In the Salmonella crosses, essentially no crossing over was detected between the E .coli genetic material on the episome and the Salmonella chromosome; therefore, the tests were complementation tests.When Salmonella strains carrying E .coli F his elements were mated with E. coli mutants, both complementation and recombination were involved in production of prototrophs.Detection of nonsense mutations: UAG and UGA nonsense mutations on E. coli F his were detected by spotting the F' strains (Table 2) on minimal agar plates spread with Salmonella