Direct selection of L-arabinose negative mutants of Escherichia coli strain B@rl.

ROSS and ENGLESBERG (1959), using three and four factor transduction exG periments with phage PI bt, found that the mutational sites of 17 L-arabinose nonutilizing mutants of Escherichia coli were arranged in a linear sequence. The 17 mutants were divided into three distinct functional groups on the basis of biochemical analyses. Complete correspondence was found between the order of the mutational sites of these mutants and their functional grouping. ENGLESBERG (1961) further defined the three groups of mutants by enzymatic analyses. It appears that two of the genetic loci (A and B) are responsible for the structures of the L-arabinose isomerase and L-ribulokinase enzymes respectively. The third locus (C) appears to be an operator gene. A fourth functional group (D) of L-arabinose nonutilizing mutants has recently been discovered. Mutants in this group (“53, ara-139) are deficient in the enzyme ~-ribulose-5-phosphate-4-epimerase, and accumulate L-ribulose-5phosphate. The growth of these mutants is strongly inhibited by L-arabinose and mutants that are relatively resistant to L-arabinose appear in their progeny with a high frequency. When one of these relatively resistant mutants was analyzed, it exhibited the characteristics of a typical Group B mutant (ENGLESBERG et al. 1962). It was postulated (ENGLESBERG et al. 1962) on the basis of these results that the L-arabinose inhibition of the Group D mutants may be directly or indirxtly related to the accumulation of ~-ribulose-5-phosphate and that relative resistance could be gained by any mutational event which prevented the accumulation of this compound. This would be accomplished by a mutation in the A or C locus as well as in the B locus. This paper will show that the sensitivity of the ora-53 mutant to L-arabinose is relieved by the occurrence of a mutation in any of the three known loci (A, B or C), so that this mutant provides a simple and direct selective system for obtaining L-arabinose negative A, B and C mutants. It will also be shown that (1) these resistant mutants are double L-arabinose negative mutants, i.e., each has a mutant site in either the A, B or C locus (“new” mutant site) in addition to the ara-53 mutant site, (2) the A, B or C mutation can be ordered within the appropriate