Duplicate genes for tyrosine transfer RNA in Escherichia coli

Abstract

Genetic and biochemical studies of Escherichia coli and the new transducing phage φ80p su III + have been used to characterize the tRNA genes of E. coli. The transducing phage stimulates the production of both su III + and su III − tyrosine tRNA upon infection, and in hybridization experiments its DNA is saturated with 1.4 tyrosine tRNA molecules per genome. One of its derivatives, selected for its genetic properties, stimulates only su III + tyrosine tRNA, and its DNA is saturated by 0.6 tyrosine tRNA molecule per genome. We conclude that the original phage carries two tyrosine tRNA genes, one su III + and one su III −, while the derivative carries a single su III + gene. The single-gene derivative apparently arises by unequal recombination involving the two genes of the original phage; the reciprocal recombination product, carrying three tyrosine tRNA genes, is also detected. Entirely analogous single-gene and three-gene derivatives of E. coli are found, and we conclude that E. coli normally carries a pair of closely-linked genes specifying its minor, or su III tyrosine tRNA.