An in vitro protein-synthesizing system (rabbit reticulocyte) was programmed with total polyadenylated messenger ribonucleic acid from wild type and various mutants in the qa gene cluster of Neurospora crassa. The products of two of the qa genes, quinate dehydrogenase (qa-3+) and dehydroshikimate dehydratase (qa-4+), were identified by specific immunoprecipitation and sodium dodecyl sulfateslab gel electrophoresis. The results indicated that for both genes induction of a specific enzyme activity by quinic acid depends on the de novo synthesis of a specific polypeptide and on the de novo appearance of specific messenger ribonucleic acid detectable by the in vitro translation assay. Furthermore, the results indicated that the appearance of this messenger ribonucleic acid is under the control of the qa-1 gene. The simplest interpretation of these results appears to be that induction of enzyme activity in the qa system is mediated by events at the transcriptional level.The qa gene cluster of Neurospora crassa contains four known genes, three of which encode three different enzymes which are induced by quinic acid and catalyze the first three reactions in the catabolism of this compound as a carbon source. The fourth gene (qa-1 +) encodes a regulatory protein which apparently acts in a positive fashion to control the synthesis of the three qa enzymes (9). The hypothesis was originally proposed, based largely on genetic evidence, that regulation of qa enzyme synthesis by the qa-1 + gene product, an activator protein, occurs at the level of transcription (10). This hypothesis is supported by evidence that induction of the qa enzymes involves de novo protein synthesis (20) Genetics 94:581, 1980).In the present paper, additional evidence for transcriptional control of two qa genes (qa-3+ and qa-4+) is presented based on studies with the rabbit reticulocyte in vitro translation system (19). This system has been programmed with total polyadenylated [poly(A)] mRNA isolated from several different strains which were either induced or uninduced for the qa enzymes by growth in the presence or absence of quinic acid, from a constitutive mutant which produces high levels of the qa enzymes in either the presence or the absence of the inducer, and from two qa-1 -mutants which are noninducible by quinic acid. The individual qa gene products (polypeptides) were subsequently 'dentified by specific immunoprecipitation and sodium dodecyl sulfate (SDS)-slab gel electrophoresis (12). The results indicate that for both the qa-3+ and qa-4+ genes, induction of a specific enzyme activity depends on the de novo synthesis of a specific polypeptide and on the de novo appearance of specific mRNA detectable by the in vitro translation assay. The results also indicate that the appearance of this mRNA is under the con-829 on May 12, 2018 by guest