Molecular cloning of the uaY regulatory gene of Aspergillus nidulans reveals a favoured region for DNA insertions.

The cloning of the positive regulatory gene, uaY, which mediates uric acid induction of enzymes and permeases of the purine degradation pathway in the fungus Aspergillus nidulans is described here. The 4 kb uaY transcript is constitutively synthesised, it is not repressed by ammonia and its transcription does not require the AreA wide-domain transcription factor. We have determined that four deletions, which have been genetically characterised, are confined to a segment of 0.9 kb. Two other deletions are double events; each is a deletion of about 1 kb plus an insertion. The positions of the deletions confine 9 out of the 11 mapped putative point mutations within a 1 kb segment. Two other non-revertible alleles, which mapped as point mutations, are insertions of at least 11 and 18 kb respectively. The pattern of gene conversion within the uaY gene was described previously. The results reported here demonstrate that conversion of sequences of at least 18 kb can occur in A. nidulans.