Positive Control of Enzyme Synthesis by Gene C in the l -Arabinose System

Abstract

Englesberg, Ellis (University of Pittsburgh, Pittsburgh, Pa.), Joseph Irr, Joseph Power, and Nancy Lee . Positive control of enzyme synthesis by gene C in the l -arabinose system. J. Bacteriol 90: 946–957. 1965.—The l -arabinose gene complex consists of genes D, A, B, and C, linked in that order between the markers thr and leu , and an unlinked gene E. Genes D, A, B, and E are the structural genes for three inducible enzymes and permease, respectively. Gene C, with two mutant alleles, C − and C c , is the regulatory gene exhibiting positive and negative control. C − mutants are deficient and C c mutants are constitutive for all three enzymes and permease. Complementation analysis, employing sexual merozygotes (A − C + × A + C − ), with six different C − mutants, demonstrates that C − is recessive to C + (positive control). A total of 61 C c mutants, isolated as clones resistant to d -fucose inhibition, are linked to the leu ara region of the chromosome, and the 22 C c mutants that were analyzed in detail mapped within the C gene among the C − mutant sites. C c mutants produce various but coordinate levels of the two enzymes measured, and permease. Complementation analysis (A − C c × A + C − , A − C c × A + C + ) shows that C c is dominant to C − (positive control) and recessive to C + (negative control). Deletion mutants that extend into the C gene are l -arabinose permease-negative, thus supporting the positive regulatory role of the C gene. The name “activator gene” is proposed for genes of the C type to accentuate their positive role in gene expression. A working model consistent with these results is presented.