A PREINDUCTION SPORULATION GENE FROM ASPERGILLUS-NIDULANS

Asexual sporulation in Aspergillus nidulans is an inducible developmental process controlled by genes that act before and after the inductive stimulus is applied. Genes that act before induction (pre-induction genes) potentially represent functions required for response to induction. This report describes the isolation and characterization of the acoB pre-induction gene which was cloned by complementation of a thermosensitive aconidial mutant followed by gene rescue. Genetic analysis and gene disruption confirmed the identity of the cloned gene. The mRNA of the acoB gene was present in uninduced vegetative hyphae, induced conidiating cultures and in both conidiospores and ascospores. An ORF in the nucleotide sequence of the acoB cDNA specifies a 327-residue protein unrelated to any known peptide sequence. Sequence analysis of the thermosensitive mutant allele. acoB202. revealed that the mutant phenotype is due to a frame-shift mutation that severely truncates the putative ACOB protein. Disruption of the acoB gene also produced a strain that was thermosensitive for conidiation. These properties suggest that acoB may be a gene that is required for sporulation only at elevated temperatures. Hybridization of acoB DNA with DNA from a variety of Aspergillus species showed that homology to this gene is largely restricted to sexually sporulating species that belong to the nidulans group.