THE ASPERGILLUS-NIDULANS BRLA REGULATORY LOCUS CONSISTS OF OVERLAPPING TRANSCRIPTION UNITS THAT ARE INDIVIDUALLY REQUIRED FOR CONIDIOPHORE DEVELOPMENT

The Aspergillus nidulans brlA locus controls conidiophore development in conjunction with the products of several other regulatory loci. In this paper, we show that the brlA locus consists of overlapping transc ription units, designated alpha and beta, with alpha transcription ini tiating within beta intronic sequences. The predicted BrlA polypeptide s differ by 23 amino acid residues at their N-termini. Targeted mutati ons specifically eliminating either the alpha or beta transcript led t o developmental abnormalities similar to those produced by previously identified hypomorphic mutants, showing that both transcripts have ess ential functions for normal development. However, provision of additio nal doses of alpha in a beta- strain or of beta in an alpha-strain rem ediated the developmental defects, indicating that the polypeptides ha ve redundant functions. It is likely that differential regulation of a lpha and beta expression in the wild type is important for the initiat ion and temporal regulation of development.