Pleiotropic deficiency in nitrogen-uptake systems and derepression of nitrogen-catabolic enzymes in npr-1 mutants of Saccharomyces cerevisiae.

The npr-1 mutation has two types of effects in Saccharomyces cerevisiae. On one hand, several nitrogen-catabolic enzymes are derepressed in the presence of ammonia, glutamine, or asparagine, which provoke their repression in a wild-type strain. On the other hand, the activity of several ammonia-sensitive permeases is decreased (from 50-100% depending on the permease considered) in npr-1 cells, independently of the nitrogen source used for growth. Our results favour the idea that the primary effect of the npr-1 mutation is on the permeases, and that the derepression of the enzymes is a consequence of the reduced uptake rate of the repressing nitrogen compounds. Hence, the product of the npr-1 gene appears to be directly involved in the development of the activity of a set of permeases which transport nitrogen compounds and which are regulated by nitrogen effectors.