Enzymes producing 4-thiouridine in Escherichia coli tRNA: approximate chromosomal locations of the genes and enzyme activities in a 4-thiouridine-deficient mutant.

A previously described mutant of Escherichia coli which lacks 4-thiouridine in its tRNA was here shown to be deficient in factor A, one of the two proteins responsible for this thiolation of uridine. Addition of exogenous factor A restored the thiolating ability of extracts prepared from the mutant. The activities of the two thiolation proteins were governed by genes at two widely separated positions on the chromosome, as determined with F-prime merodiploids. The site governing factor A activity lay roughly in the region of the recently reported position of nuv, a gene controlling the production of 4-thiouridine in tRNA.