Chromosomal heteromorphism linked to the mating type locus of the oomycetePhytophthora infestans

Sporulation in Saccharomyces cerevisiae normally occurs only in MATa/MAT alpha diploids. We show that mutations in RME1 bypassed the requirements for both a and alpha mating type information in sporulation and therefore allowed MATa/MATa and MAT alpha/MAT alpha diploids to sporulate. RME1 was located on chromosome VII, between LEU1 and ADE6.

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Transformation of protoplasted yeast cells is directly associated with cell fusion

Molecular and Cellular Biology ◽

10.1128/mcb.4.4.771-778.1984 ◽

1984 ◽

Vol 4 (4) ◽

pp. 771-778

Author(s):

S Harashima ◽

A Takagi ◽

Y Oshima

Keyword(s):

Cell Fusion ◽

Mating Type ◽

Nuclear Fusion ◽

Yeast Cells ◽

Nuclear Markers ◽

Type Locus ◽

Mating Type Locus ◽

Yeast Protoplasts ◽

Yeast Plasmids ◽

Binominal Distribution

The frequency of cell fusion during transformation of yeast protoplasts with various yeast plasmids with a chromosome replicon (YRp or YCp) or 2 mu DNA (YEp) was estimated by two methods. In one method, a mixture of protoplasts of two haploid strains with identical mating type and complementary auxotrophic nuclear markers with or without cytoplasmic markers was transformed. When the number of various phenotypic classes of transformants for the nuclear markers was analyzed by equations derived from binominal distribution theory, the frequency of nuclear fusion among the transformants was 42 to 100% in transformations with the YRp or YCp plasmids and 28 to 39% with the YEp plasmids. In another method, a haploid bearing the sir mutation, which allows a diploid (or polyploid) homozygous for the MAT (mating type) locus to sporulate by the expression of the silent mating-type loci HML and HMR, was transformed with the plasmids. Sporulation ability was found in 43 to 95% of the transformants with the YRp or YCp plasmids, and 26 to 31% of the YEp transformants. When cytoplasmic mixing was included with the nuclear fusion, 96 to 100% of the transformants were found to be cell fusants. Based upon these observations, we concluded that transformation of yeast protoplasts is directly associated with cell fusion.

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INTERCONVERSION OF YEAST MATING TYPES II. RESTORATION OF MATING ABILITY TO STERILE MUTANTS IN HOMOTHALLIC AND HETEROTHALLIC STRAINS

Genetics ◽

10.1093/genetics/85.3.373 ◽

1977 ◽

Vol 85 (3) ◽

pp. 373A-393

Author(s):

James B Hicks ◽

Ira Herskowitz

Keyword(s):

Saccharomyces Cerevisiae ◽

Mating Type ◽

Yeast Cells ◽

Mating Types ◽

Yeast Saccharomyces Cerevisiae ◽

Type Locus ◽

Mating Ability ◽

Mating Type Locus ◽

Regulatory Information ◽

Ho Gene

ABSTRACT The two mating types of the yeast Saccharomyces cerevisiae can be interconverted in both homothallic and heterothallic strains. Previous work indicates that all yeast cells contain the information to be both a and α and that the HO gene (in homothallic strains) promotes a change in mating type by causing a change at the mating type locus itself. In both heterothallic and homothallic strains, a defective α mating type locus can be converted to a functional a locus and subsequently to a functional α locus. In contrast, action of the HO gene does not restore mating ability to a strain defective in another gene for mating which is not at the mating type locus. These observations indicate that a yeast cell contains an additional copy (or copies) of α information, and lead to the "cassette" model for mating type interconversion. In this model, HM a and hmα loci are blocs of unexpressed α regulatory information, and HMα and hm a loci are blocs of unexpressed a regulatory information. These blocs are silent because they lack an essential site for expression, and become active upon insertion of this information (or a copy of the information) into the mating type locus by action of the HO gene.

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