A partial deletion map of the galactose operon inE. coliK12

Abstract

We have isolated a number of λdgHFT lysates which carry proximal fragments of the galactose operon. Most of these have been shown to be different, and each terminates in either the kinase or transferase cistron. They divide the kinase cistron genetically into seven blocks of mutants, and the transferase into eight.When a λdgis used to transduce a bacterium which carries a mutation in a cistron which is intact in the λdgthe transduction frequency is high in the presence of λ-helper. This is attributed to integration of the transducing fragment at the λ-attachment site and complementation between the two operons in the heterogenote. When the same λdgtransduces a mutation lying in the cistron in which the λdgterminates, so that recombination within the galactose operon is obligatory, the transduction frequency is 10 to 1000 times less.In such cases there is a general increase in transduction frequency between distal mutations (i.e. those lying near the termination of the deletion) and proximal mutations, but the relationship does not hold for many individual pairs of mutants, probably due to physiological differences between the bacterial strains.