Section Molecular Genetics of Industrial Microorganisms, Wageningen Agriculturál University, The Netherlands.
A fortuitously cloned 3'-truncated cDNA encoding the Agaricus bisporus delta 1-pyrroline-5-carboxylate dehydrogenase was used to characterize the complete gene. The gene would encode a cytosolic polypeptide of 546 amino acids, and the basidiomycetous gene was evenly expressed in various parts of the mushroom except for the gills. No expression was detected in compost-grown mycelium. The steady-state mRNA level of the gene in the vegetative phase was determined on simple synthetic media and was two- to threefold higher with ammonium or proline as the sole nitrogen source compared to glutamate as the sole nitrogen source. Moreover, the steady-state mRNA level was not markedly influenced by addition of ammonium phosphate to proline- or glutamate-utilizing cultures. The results suggest that ammonium and the amino acids proline and glutamate are equally preferred nitrogen sources in this organism and are consistent with previous observations of H. M Kalisz, D.A. Wood, and D. Moore (Trans. Br. Mycol. Soc. 88:221-227, 1987) that A. bisporus continues to degrade protein and secrete ammonium even if ammonium and glucose are present in the culture medium.