MEIOTIC TRANSVECTION IN FUNGI

The Neurospora crassa Asm-1(+) (ascospore maturation 1) gene encodes a n abundant nucleus-localized protein required for formation of female structures and for ascospore maturation. Deletion mutants of Asm-1(+) are ''ascus-dominant,'' i.e., when crossed to wild type, neither Asm-1 (+) nor Asm-1(Delta) spores mature. To explain this behavior, we consi dered three models: an effect of reduced dosage of the gene product, f ailure of internuclear communication, and failure of transvection (reg ulation dependent on pairing of alleles). We found that for proper reg ulation of subsequent sexual sporulation, Asm-1(+) must be in proximit y, probably paired, to its allelic counterpart in the zygote: i.e., tr ansvection must occur. Disruption of pairing causes failure of ascospo re progeny to mature. Transvection in Neurospora, unlike in Drosophila , occurs immediately before meiosis, and can be demonstrated between w ildtype alleles.