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 transcription units, designated alpha and beta, with alpha transcription initiating within beta intronic sequences. The predicted BrlA polypeptides differ by 23 amino acid residues at their N-termini. Targeted mutations specifically eliminating either the alpha or beta transcript led to developmental abnormalities similar to those produced by previously identified hypomorphic mutants, showing that both transcripts have essential functions for normal development. However, provision of additional doses of alpha in a beta- strain or of beta in an alpha-strain remediated the developmental defects, indicating that the polypeptides have redundant functions. It is likely that differential regulation of alpha and beta expression in the wild type is important for the initiation and temporal regulation of development.