Biotecnologia Aplicada Elfos Scientiae ISSN: 0684-4551 Vol. 13, Num. 3, 1996, pp. 212

CARBON CATABOLITE REPRESSION IN Aspergillus nidulans

Beatriz Cubero, Martine Mathieu, Ramon Gonzalez, Dennis Gomez, Victoria Gavrias, Cristina Panozzo, Beatrice Felenbok and Claudio Scazzocchio

Institut de Genetique et Microbiologie, Universite Paris Sud, 91405, Orsay, France.

Code Number:BA96090
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Repression of the ethanol regulon is independent of the nitrogen source, on the other hand, repression of the proline gene cluster is only achieved when both a nitrogen and repressing carbon source are present. Repression of the proline gene cluster acts directly on the structural genes, repression of the specific regulatory gene is marginal and of no physiological significance.

The ethanol regulon is controlled by a double lock mechanism, drastic repression of the specific, positive-acting regulatory gene and direct repression of the structural genes. We have carried a limited mutational analysis of the creA gene. We have identified mutations on the promoter, in the DNA binding domain and in the carboxy-terminus of the protein. The binding sites have been determined in vitro. The consensus sequence recognized by the creA Zn fingers is 5'SYGGRG3'. Classical and reverse genetical experiments have been carried out to determine, among a multitude of sites, those which are of physiological importance.

The data shows that creA acts in rather different ways in the two systems. In the ethanol regulon it prevents the binding of or activation by the positively-acting, specific alcR protein. This mechanism acts both on expression of the alcR gene itself and of the structural gene alcA. In the proline cluster it acts by preventing the activity of a different, and possibly general transcription factor. This explains the particular interaction of carbon and nitrogen metabolite repression found in this system. The site of action of this new factor has been narrowed down to 600 bp in the intergenic region between the divergently transcribed prnD (proline oxidase) and prnB (proline permease) genes. The creA protein does not prevent directly the binding of this new, positive acting, transcription factor.

Copyright 1996 Elfos Scientiae