Reversions of the L-ribulokinase structural gene of Escherichia coli.

B C 28’ 22’ 15 I eu --79 6 16’ 74 70 26 43 23 63 71 60 14 62 80 55 46 25 I 29. 24 8 27 M U T A T I O N S in the araB gene, the structural gene for L-ribulokinase, of the arabinose gene-complex in Escherichia coli B/r (Figure 1) produce a twofold effect (ENGLESBERG 1961; LEE and ENGLESBERG 1962, 1963): they are deficient in L-ribulokinase, and they differ in their level of L-arabinose isomerase and ~-ribulose-5-phosphate-4-epimerase, the products of the adjacent structural araA and araD genes. Certain araB mutants show a higher inducible level of isomerase and epimerase than the wild type while others show less. In addition, the levels of the isomerase and epimerase enzymes of each araB mutant are COordinated. The L-arabinose isomerase produced by the araB mutants is indistinguishable from the isomerase produced by the wild-type strain of E , coli. A genetic map of the araB gene fails to show any relationship between the relative location of the mutant sites and their isomerase activity ( CRIBBS and ENGLESBERG 1964). In this study, the araB mutants were further examined to determine if the mutants which produced approximately the same levels of isomerase were results of the same type of genetic alteration. Since certain chemical mutagens, particularly base analogues, have been considered to induce specific types of nucleotide