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A mutant (nit8) with a lowered activity of glutamine synthetase (GS) was isolated in Aspergillus nidulans. The levels of GS and of an arginine catabolic enzyme, ornithine transaminase (OTA) were assayed under a variety of growth conditions leading to repression, depression and induction of OTA in the wild type, nit8 and several regulatory mutants. The results obtained appear to exclude the possibility of involvement of GS in the regulation of arginine catabolism in A. nidulans.
Sensitive assays of histidase activity were used to follow the production of this enzyme as directed by a gene newly introduced into cells of Bacillus subtilis by transformation. Histidase activity can be detected in histidase-negative recipient cells within 1 hr after the addition of deoxyribonucleic acid extracted from histidase-positive donors. Enzyme production continues for one to two additional hours and then ceases. Histidase production in the transformed cells is fully sensitive to catabolite repression. Catabolite repression is rapidly established after transformation of recipient cells that are resistant to this form of regulation.
Analyzes the mechanism of catabolite repression of grampositive and gramnegative bacteria. The role of cyclic adenosine monophosphate and CRP protein, forming a complex, is shown. Contribution of ATP kinase to manifestation of the catabolic repression phenomenon in grampositive bacteria is discussed.
The structural gene for yeast fructose-1,6-bisphosphatase (FbPase) has been cloned by complementation of a strain carrying the fbp1-1 mutation and lacking FbPase activity. By Northern analysis it could be shown that the fbp1-1 mutation does not interfere with the transcription of the gene although no normal active enzyme is produced. Strains transformed with the cloned gene on a multicopy plasmid overproduce FbPase but are still subject to strong catabolite repression. Catabolite inactivation, however, is slowed down in such strains.
Overproduction of microbial metabolites is related to developmental phases of microorganisms. Inducers, effectors, inhibitors and various signal molecules play a role in different types of overproduction. Primary and secondary metabolism are interconnected. Biosynthesis of enzymes catalyzing metabolic reactions in microbial cells is controlled by well-known positive and negative mechanisms, e.g. induction, repression, catabolite repression, mechanisms controlling enzyme activity include isosteric and allosteric interactions, e.g. competitive and non-competitive inhibition, allosteric effects, molecular conversion etc. Biosynthesis of secondary metabolites is catalyzed by unaltered enzymes of primary metabolism, by altered enzymes of primary metabolism and by specific enzymes of secondary metabolism. In addition to classical mutagenesis and selection of suitable microbial cells, methods of molecular genetics are used in the overproduction of microbial products.
The gntT gene of Escherichia coli is specifically induced by gluconate and repressed via catabolite repression. Thus, gluconate is both an inducer and a repressor of gntT expression since gluconate is a catabolite-repressing sugar. In a gntR deletion mutant, the expression of a chromosomal gntT::lacZ fusion is both high and constitutive, confirming that GntR is the negative regulator of gntT. Indeed, GntR binds to two consensus gnt operator sites; one overlaps the -10 region of the gntT promoter, and the other is centered at +120 with respect to the transcriptional start site. The binding of GntR to these sites was proven in vitro by gel redardation assays and in vivo by site-directed mutagenesis of the binding sites. Binding of GntR to the operators is eliminated by gluconate and also by 6-phosphogluconate at a 10-fold-higher concentration. Interestingly, when gntR deletion strains are grown in the presence of gluconate, there is a twofold decrease in gntT expression which is independent of catabolite repression and binding of GntR to the operator sites. This novel response of gntR mutants to the inducer is termed ultrarepression. Transcription of gntT is activated by binding of the cyclic AMP (cAMP)-cAMP receptor protein (CRP) complex to a CRP binding site positioned at -71 upstream of the gntT transcription start site.