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

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Abstract
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 Cc, is the regulatory gene exhibiting positive and negative control. C- mutants are deficient and Cc mutants are constitutive for all three enzymes and permease. Complementation analysis, employing sexual merozygotes (A-C+ X A+C-), with six different C-mutants, demonstrates that C- is recessive to C+ (positive control). A total of 61 Cc mutants, isolated as clones resistant to D-fucose inhibition, are linked to the leu ara region of the chromosome, and the 22 Cc mutants that were analyzed in detail mapped within the C gene among the C- mutant sites. Cc mutants produce various but coordinate levels of the two enzymes measured, and permease. Complementation analysis (A-Cc X A+C-, A-C X A+C+) shows that C is dominant to C" (positive control) and recessive to C+ (negative control). Deletion mutants that extend into the C gene are L-arabinose per-mease-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.

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