Organization of a gene cluster expressed specifically in the asexual spores of A. nidulans

Abstract

The organization and regulation of a 13.3 kilobase region of the A. nidulans genome that is preferentially expressed during conidiophore development were studied. This cloned DNA segment codes for 6 polysomal poly(A)+ RNA present in dormant asexual spores (conidia) at 8-50 copies per cell. The genes encoding these RNA occur once per haploid genome, are separate and distinct, appear to be co-linear with their mature RNA products and are present in both polarities. Two of the genes have short regions of homology near their 5'' ends, but otherwise the segment is internally unique. All of the RNA are absent from, or present at very low levels in, wild-type somatic cells (hyphae) and developing cultures of asporogenous mutant strains. In synchronously conidiating wild-type cultures, each of the RNA can first be detected at a time coinciding with the appearance of mature spores. Thus this region comprises a cluster of tightly linked, discrete genes, which are all expressed at the same time, but not to the same extent, in a single differentiating cell type.