Fine Structure Mapping by Complete Transduction between Histidine-Requiring Salmonella Mutants.

SUMMARY: The growth characteristics, accumulations and genetic tests carried out by means of complete transduction for over 200 independently isolated histidine-requiring (his) mutants of Salmonella typhimurium are described. Sites of mutation engendering the histidine-requiring phenotype all lie within a short chromosomal region. This region is divisible into seven smaller regions, or gene loci, each correlated with a specific physiological phenotype. The gene loci appear to be linearly arranged and are linked in the order E, F, A, B, C, D and G. The five central loci are linked in an order corresponding to the sequence of reactions in the biosynthetic pathway for histidine. The functions of the two terminal loci, E and G, are unknown. The loci are nearly, or truly adjacent. A few of the sites of mutation are accurately mapped within a single gene. All the evidence is consistent with the view that processes involved in intra- and inter-genic recombination are identical. Some characteristics of multisite mutations are described. Several multisite mutations are interpreted as due to deletion of genetic material while one (his-57) is interpreted as due to an inversion, with or without concomitant deletion of an adjacent region. Single-site and multisite mutations exert specific effects on recombination frequencies in nearby regions.