Using one of 17 expressed sequence tags (ESTs) previously identified as specific to the late sexual developmental (LSD) stage of Aspergillus nidulans, a gene for the subject EST was isolated. The determined DNA sequences revealed an open reading frame encoding a 356 amino acid polypeptide which does not share a sequence similarity to previously identified genes or proteins. The isolated gene was named lsdA (late sexual development), since it was expressed abundantly at the LSD stage. The lsdA gene expression began earlier than at the LSD stage. Disruption of the lsdA gene in the veA+ background strongly induced sexual development under conditions where sexual development in wild-type strains is almost completely inhibited. In contrast, in the veA1 background, an lsdA null mutant failed to show any phenotypic difference in sexual development under the various conditions tested. These results indicate that the lsdA gene may be responsible for inhibiting the sexual development of veA+ strains by a high concentration of a salt.