Judith Stamberg

The organisation of the incompatibility factors in higher fungi: The effect of structure and symmetry on breeding

SummaryAn evaluation of the structure of incompatibility systems in the higher fungi and its effect on inbreeding and outbreeding indicates that: In unifactorial systems a one-locus structure, which permits 50 per cent, inbreeding, is preferable to a two-locus structure, which would permit inbreeding to rise above 50 per cent. In bifactorial systems a two-locus structure for each factor is advantageous because it makes possible a high outbreeding potential with a small number of alleles. The two-locus structure also confers flexibility on the inbreeding potential. A symmetrical distribution of alleles among the four loci of a two-locus bifactorial system allows for maximal outbreeding. The advantage of symmetry is most pronounced when the total number of allelic specificities is not large. The asymmetrical distribution of alleles among the four incompatibility loci of Schizophyllum commune suggests that its incompatibility system evolved from a one-locus unifactorial system. The Aß locus, with 32 alleles, is assumed to be the oldest locus; the remaining three loci, with 9 alleles each, are assumed to have come into operation within a short time of each other, at a later stage.

Meiosis as a source of spontaneous mutations in schizophyllum commune

Spontaneous mutation frequencies were determined for two loci in the fungus Schizophyllum commune, at meiosis and at mitosis. For both loci the meiotic frequency is significantly higher than the mitotic frequency. No correlation was found between meiotic mutagenesis and recombination of markers bracketing the mutant site. The meiotic temperature affected the spontaneous mutation frequency but not the recombination frequency in the cross examined. A number of suppressor mutations were detected for both loci examined. Almost all the suppressors are closely linked to the site they suppress. The distribution of mutations among the suppressor sites was different at meiosis and at mitosis.

Meiosis in Schizophyllum commune: premeiotic DNA replication and meiotic synchrony induced with hydroxyurea.

Hydroxyurea (HU) effectively inhibits meiosis in Schizophyllum . The predominant cytological stage in inhibited fruit bodies is fusion. The inhibition is reversible and makes possible synchronization of a naturally nonsynchronous system. Microphotometric determinations of the DNA content in prefusion nuclei treated with HU suggest that premeiotic DNA replication occurs in prefusion nuclei. Synaptinemal complexes are not completed in HU-treated nuclei, suggesting that this event is dependent on premeiotic DNA replication.

Selectively recombining B incompatibility factors of Schizophyllum commune

SummaryAnalysis of genetic crosses among strains of Schizophyllum commune carrying recombining B factors has revealed that not all heteroallelic pairs of B factors are able to recombine with each other. This suppression of recombination is highly specific and appears to be determined by the B factors themselves.

Meiosis in Schizophyllum commune: the effect of hydroxyurea on basidiospore sporulation, germination, and nuclear number.

SummaryIn a search for an experimental procedure to synchronize meiosis in fruit bodies of Schizophyllum commune, the effect of hydroxyurea on sporulation was tested. Results indicate that hydroxyurea has an immediate and reversible effect on basidiospore sporulation, germination, and nuclear number. A tentative time schedule for meiosis is presented.

Deletion mapping of wildtype and mutant alleles at the B incompatibility factor of Schizophyllum

SummaryStrains of Schizophyllum commune carrying mutations at the Bβ incompatibility locus were crossed to strains with wildtype Bβ alleles to determine the recombinational spectra of the mutations. An excellent correlation between recombining ability and mating behavior supports the hypothesis that many wildtype and mutant alleles are associated with deletions and that the degree of impairment of recombination and mating interaction reflects the size of the deletion.

Selection with cycloheximide of metabolic acid UV-sensitive mutants of Schizophyllum commune and Saccharomyces cerevisiae

The difference in lethality to cycloheximide between actively dividing and non-dividing cells was exploited to enhance detection of auxotrophic and UV-sensitive mutants in the fungi Schizophyllum commune and Saccharomyces cerevisiae.

Recombinational analysis of mutations at an incompatibility locus of Schizophyllum

SummaryStrains of Schizophyllum commune carrying mutations at the Bβ incompatibility locus were crossed to wildtype strains to determine the recombinational spectra of the mutations. The results indicate a correlation between recombining ability and mating behavior which can be explained if some of the mutations are associated with deletions. The failure to recover recombinants in crosses between these mutations and certain natural Bα alleles supports the hypothesis that naturally occurring incompatibility alleles arose by deletion.

Repair of UV-induced damage in wild-type and mutant strains of schizophyllum commune

The basidiomycete fungus Schizophyllum commune was found to have both photo-repair and dark-repair systems for UV-induced damage. Three UV-sensitive mutants were isolated and characterized for ability to repair UV-induced damage in light and dark, and for cross-sensitivity to caffeine and methyl methanesulfonate. Two of the mutants were damaged, to different extents, in their capacity for excision repair; one of these mutants was also probably damaged in post-replication repair. The third mutant was damaged only in post-replication repair.

Three tests for shared allelic specificities in the B incompatibility factor of Schizophyllum commune

The incompatibility factors of Schizophyllum commune are each composed of two loci. Several authors have suggested that one locus arose as a duplication of the other, implying that the two loci of a factor have at least one allele in common. Three tests for the detection of such shared specificities in one incompatibility factor are presented here. The data indicate that no alleles are shared by the two loci composing this factor.