Altered dihydrofolate reductase in fol regulatroy mutants of Escherichia coli K12.

Summary Culture of the thymine-dependent mutant of Rhizobium trifolii T37 was synchronized with phenethanol. During bacterial synchronous growth with synchronized replication of DNA, cells were differentially labeled using subsequently ³H-thymidine of low and high specific activity. The grain tracks produced in autoradiographs of chromosomes were denser on both ends than in the middle. In control experiments with bacteria labeled only with ³H-thymidine of low specific activity, the grain density was uniform throughout the grain track. The results constitute clear evidence of bidirectional replication of R. trifolli chromosome.