Developmental and metabolic regulation of the phosphoglucomutase-encoding gene, pgmB, of Aspergillus nidulans

We have isolated the pgmB gene from Aspergillus nidulans, which encodes a p hosphoglucomutase, one of the key enzymes in carbohydrate metabolism. The p gmB gene is located on chromosome VII and its ORF encodes 557 amino acids. Mutant phenotypes were analysed by expression of high levels of pgmB antise nse RNA, which lead to a loss of detectable levels of sense RNA. Under cond itions of antisense RNA expression, a 30% reduction in the growth rate was observed in comparison to wild-type. On the enzyme level, expression of pgm B antisense RNA resulted in a 35% reduction in total phosphoglucomutase act ivity. Two pgmB mRNAs were observed under all conditions tested and differ with respect to the location of the poly(A) site. Expression of pgmB driven by the GAL1 promoter in Saccharomyces cerevisiae complemented the growth p henotype of a pgm2 Delta mutant strain and suppressed the sensitivity of a gcn4 Delta mutant strain to amino acid starvation in the presence of galact ose. Cultivation of A. nidulans in the presence of glucose or galactose as carbon source did not affect transcription of pgmB. However, amino acid sta rvation conditions resulted in a six-fold reduction in the level of pgmB mR NA, while genes for amino acid biosynthesis showed increased transcription. Transcription of pgmB was low during hyphal growth and in the sexual phase of development, but was significantly increased during the asexual stage o f the A. nidulans life cycle.