No abstract

The size and extent of four Neurospora crassa duplications, Dp(AR17), Dp(IBj5), Dp(OY329), and Dp(B362i), was determined by testing the coverage of RFLP markers. The first three duplications were all .350 kb and have been shown in earlier studies to act as dominant suppressors of repeat-induced point mutation (RIP) in gene-sized duplications, possibly via titration of the RIP machinery. Dp(B362i), which is only 117 kb long, failed to suppress RIP. RIP suppression in gene-sized duplications by large duplications was demonstrated using another test gene, dow, and supposedly applies generally. Crosses homozygous for Dp(AR17) or Dp(IBj5) were as barren as heterozygous crosses. Barrenness of the heterozygous but not the homozygous crosses was suppressible by Sad-1, a semidominant suppressor of RNAi-dependent meiotic silencing by unpaired DNA. A model is proposed in which large duplications recessively suppress semidominant Sad-1 mutations. The wild-isolated Sugartown strain is hypothesized to contain a duplication that confers not only dominant suppression of RIP but also a barren phenotype, which is linked (9%) to supercontig 7.118 in LG VII.

Null mutations were generated in the erg-3 gene of Neurospora crassa by repeat-induced point mutation (RIP). The mutants were viable, lacked ergosterol, were resistant to the steroidal glycoside a-tomatine and were sensitive to the phytoalexins pisatin and biochanin A. RIP was frequently associated with silencing of the hph gene located adjacent to the duplicated erg-3 sequence. The silencing of hph was reversible in the two cases examined and appeared to be due to the spread of cytosine methylation associated with RIP. The erg-3 mutant could be complemented by transformation with recombinant genes that encode proteins chimeric for amino acid sequences from the transmembrane (TM) domain of human lamin B receptor (LBR). This indicates that the LBR T M domain possesses A14n15-red~cta~e activity.

No abstract

No abstract