l -ARABINOSE-SENSITIVE, l -RIBULOSE 5-PHOSPHATE 4-EPIMERASE-DEFICIENT MUTANTS OF ESCHERICHIA COLI

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Abstract
Englesberg , E. (University of Pittsburgh, Pittsburgh, Pa.), R L. Anderson, R. Weinberg, N. Lee, P. Hoffee, G. Huttenhauer, and H. Boyer . l -Arabinose-sensitive, l -ribulose 5-phosphate 4-epimerase-deficient mutants of Escherichia coli . J. Bacteriol. 84: 137–146. 1962— l -Arabinose-negative mutants of Escherichia coli B/r, ara-53 and ara-139, are deficient in the enzyme l -ribulose 5-phosphate 4-epimerase; ara-53, further analyzed, accumulates large quantities of l -ribulose 5-phosphate when incubated with l -arabinose. The mutant sites are closely linked to the left of the previously ordered l -arabinose mutant sites, and probably represent the structural gene for l -ribulose 5-phosphate 4-epimerase (gene D) in the l -arabinose operon. The inducible levels of l -arabinose isomerase and l -ribulose 5-phosphate 4-epimerase vary correspondingly as a result of mutation in the structural gene for l -ribulokinase (gene B), further substantiating the dual structural and regulatory function of this gene locus. Ara-53 and ara-139 are strongly inhibited by l -arabinose and give rise to l -arabinose-resistant mutants. The one resistant mutant analyzed still lacks the 4-epimerase but is deficient in l -ribulokinase and has increased l -arabinose isomerase activity, a characteristic of a type of mutation in the B gene. It is proposed that accumulation of l -ribulose 5-phosphate is responsible for the inhibition, and that mutation to resistance will involve mutation in the A, B, C, permease, or repressor genes, thus providing a direct method for isolating these types of l -arabinose-negative mutants. Glucose prevents and cures the l -arabinose inhibition.