THE ORIGIN OF STERILE CYTODUCTANTS OBTAINED
IN THE ALPHA-TEST
Shiriaeva A.A.1, Andreychuck Y.V.1, Zhuk A.S.1,2, Stepchenkova E.I.1,2, Inge-Vechtomov
S.G.1,2
1
Saint-Petersburg State University, St.Petersburg
2
Saint-Petersburg Branch of Vavilov Institute of General Genetics, RAS, St.Petersburg,
Russia
The alpha-test is a sensitive system for genetic toxicology. The system utilizes
heterotallic strains of yeast Saccharomyces cerevisiae. It is based on genetic system
controlling the mating type in yeast. The mating type of yeast strains is controlled by the
MAT locus which is located on the right arm of chromosome III. The MAT locus
determines “a” or “α” cell type of haploid cells. Normally haploids of the opposite cell
types can mate and form diploid cells. Primary lesions, mutations and recombination
events in MATα as well as loss of the chromosome III or its right arm impair the MATα
expression. It causes mating type switch from α to a and mating of two initially α-type
cells. The frequency of the "illegitimate" hybridization is a criterion of genome
instability in the alpha-test.
Different phenotypes of hybrids in the alpha-test correspond to different molecular
events of the mating type switch. It was predicted that sterile cells obtained in
"illegitimate" cytoduction (the modification of the alpha-test) contain mutations in the
MATα locus. Our new data indicate that two thirds of sterile cytoductants do hold
mutations in the MATα. We demonstrate that the other sterile cells are different in their
ploidy. One of the reasons for sterility is forming of triploid cells α/a/α. We show that
overexpression of STE12 transcription factor restores mating type “α” to triploid cells
α/a/α as well as to diploid cells α/a. Our findings open new opportunities for further
improvement of the alpha-test.
Acknowledgements: Grant RFBR # 15-04-08625 and Research Grant of St. Petersburg
State University #1.38.426.2015.