RESUMO
The structure of the amdS gene of Aspergillus nidulans has been determined by nucleotide sequence analysis. The coding sequence is interrupted by three small introns with splicing signals consistent with other fungal genes. Possible TATA and CAAT elements are found upstream of the start point of transcription. Sequence changes in mutations in the 5' region of the gene have been determined. Two deletions including the start point of transcription abolish detectable transcripts. A series of mutations in the first exon cause frame shifts leading to polypeptide chain termination in the N-terminal region of the polypeptide. Levels of amdS RNA are reduced in these mutants indicating that translational termination can lead to decreased transcription or (more probably) to lower mRNA stability. The amdI18 mutation has properties consistent with it having a general up-promoter effect on amdS expression and results from a single base pair substitution approx. 77 bp upstream from the transcription start point.