Suppression of a missense mutation in the L-ribulokinase gene of Escherichia coli.

HE L-arabinose gene-enzyme complex, except for the unlinked L-arabinose Tpermease gene, araE, is shown in Figure 1. araB and araA are the structural genes for the L-ribulokinase and L-arabinose isomerase, respectively; while araD is probably the structural gene for ~-ribulose-5-phosphate-4-epimerase ( ENGLESBERG 1961 ; ENGLESBERG et al. 1962; LEE and ENGLESBERG 1962,1963). The ma€ gene is a regulatory gene, and its product regulates, in a positive manner, the expression of the maD, araA, araB and araE structural genes (ENGLESBERG, IRR, POWER, and LEE 1965; SHEPPARD and ENGLESBERG 1967). Transcription of the three adjacent structural genes begins at an initiator region located between the araB and araC genes (ENGLESBERG, IRR, POWER, and LEE 1965). Thus, the order of transcription, as well as translation, of these linked structural genes is presumably araB, araA and araD. In a previous study (CRIBBS 1965) a number of araB revertants were isolated that utilized L-arabinose at a slower rate than the wild type. Transduction analyses of these partial revertants indicated the presence of both the original araB mutation and a suppressor mutation. These suppressor mutations were either closely linked, or were not co-transducible (i.e. unlinked) with, the araB gene. When the suppressor was not present in the genome, the araB mutation prevented production of a functional L-ribulokinase. However, a suppressed araB revertant has been isolated that can use L-arabinose