The early events of macrocyst development in Dictyostelium discoideum have been investigated using a new culturing system. When cells of opposite mating-types, HM1 and NC4, are cultured together at the appropriate temperature in the dark, giant cells appear, ingest the surrounding amoebae, and develop into macrocysts. Although these giant cells have been assumed to be the products of the fusion...

Mating type genes regulate sexual compatibility and sexual reproduction in fungi. This review focuses on recent molecular analyses of well-characterized mating systems from representative ascomycete (Neurospora crassa, Podospora anserina) and basidiomycete (Ustilago maydis, Coprinus cinereus, Schizophyllum commune) fungi. These mating systems include many conserved components, such as gene regu...

Haploid budding yeast has two mating types, defined by the alleles of the MAT locus, MATa and MATα. Two haploid cells of opposite mating types mate by signaling to each other using reciprocal pheromones and receptors, polarizing and growing toward each other, and eventually fusing to form a single diploid cell. The pheromones and receptors are necessary and sufficient to define a mating type, b...

In Chlamydomonas reinhardtii, chloroplast genomes are normally transmitted by the mating type plus (mt+) parent and mitochondrial genomes by the mating type minus (mt-) parent. In this paper we describe three new nuclear mutations, designated mat-3-1 to -3, which are tightly linked to the mt+ allele and permit high transmission of chloroplast genomes from the mt- parent, but have no effect on t...

Eukaryotes have acquired many mechanisms to repair DNA double-strand breaks (DSBs) [1]. In the yeast Saccharomyces cerevisiae, this damage can be repaired either by homologous recombination, which depends on the Rad52 protein, or by non-homologous end-joining (NHEJ), which depends on the proteins yKu70 and yKu80 [2] [3]. How do cells choose which repair pathway to use? Deletions of the SIR2, SI...

Colonies of Schizosaccharomyces pombe that contain ascospores (e.g., colonies of homothallic strains) turn black after treatment with iodine vapors. Heterothallic strains of S. pombe normally do not show this reaction. In experiments with the latter strains we found mutants which exhibit a positive iodine reaction though they do not contain ascospores. This phenotype is due to mutations in a ne...

To explore the similarities and differences of regulatory circuits among budding yeasts, we characterized the role of unscheduled meiotic gene expression 6 (UME6) and a novel mating type switching pathway in Kluyveromyces lactis. We found that Ume6 was required for transcriptional silencing of the cryptic mating-type loci HML and HMRa. Ume6 acted directly at these loci by binding to the cis-re...

Intratetrad mating, the fusion of gametes formed in a single meiosis, has unusual consequences for genetic diversity, especially in genome regions linked to mating type loci. Here we investigate the fate of modifier alleles that alter the rate of intratetrad mating, under models of heterozygote advantage and of genetic load resulting from recurrent mutation. In both cases, intratetrad mating is...

Many interspecies hybrids have been discovered in yeasts, but most of these hybrids are asexual and can replicate only mitotically. Whole-genome duplication has been proposed as a mechanism by which interspecies hybrids can regain fertility, restoring their ability to perform meiosis and sporulate. Here, we show that this process occurred naturally during the evolution of Zygosaccharomyces para...