MOLECULAR CHARACTERIZATION OF THE GLNA GENE ENCODING GLUTAMINE-SYNTHETASE FROM THE EDIBLE MUSHROOM AGARICUS-BISPORUS

The gene encoding glutamine synthetase (glnA) was isolated from an Aga ricus bisporus H39 recombinant lambda phage library. The deduced A. bi sporus glutamine synthetase amino acid sequence contains 354 residues. The amino acid sequence is very similar to that derived from the gene coding for glutamine synthetase of the yeast Saccharomyces cerevisiae . The open reading frame is interrupted by four introns. Northern anal ysis revealed that transcription of the gene is repressed upon additio n of ammonium to the culture but the repression was not as strong as t hat of the gene encoding NADP(+)-dependent glutamate dehydrogenase (gd hA). Enzyme activities are low in the presence of ammonium, glutamine and albumin and do not correlate with the mRNA levels revealed by Nort hern analysis. This suggests that glutamine synthetase expression in A . bisporus is also post-transcriptionally regulated by the nitrogen so urce.