Isolation and Identification of Yeasts from Natural ... - Library Science

CHAPTER 4
Rare-Mating and Cytoduction
in Saccharomyces cerevisiae
John F. T. Spencer and Dorothy M. Spencer
1. Introduction
Rare-mating is an adaptation of techniques used for normal classical
mating in yeasts. It was first used to study the switching of mating types
in Saccharomyces cerevisiae by Gunge and Nakatomi (I), but was later
adapted to the investigation of industrial yeasts that have low mating
frequencies and low spore viabilities, or that do not mate or sporulate at
all (2). The method depends on the fact that occasional mating-type
switching occurs in industrial yeasts, which are normally diploids or of
higher ploidy, and may display aneuploidy as well. This results in the
occurrence at low frequency of mating cells, that can then conjugate with
a known laboratory mating strain of either a or a mating type (or aa or
aa mating type), and whose progeny then carry the auxotrophic or other
markers present in the laboratory strain. In addition, the ability to sporu-
late, in the progeny, is often enhanced, so that genetic analysis can be
carried out on the strain, and some idea of the nature of the genome of the
industrial strain can be obtained.
Cytoduction is the transfer of subcellular organelles, such as mito-
chondria and/or killer virus-like particles (VLPs) from one strain of yeast
to another, without transferring any nuclear genes. This can be done by
fusing or mating a strain carrying a karl-1 mutation, with the strain that
is to be used as the donor of the organelles, isolating strains carrying the
karl-1 nucleus and the organelles, and fusing cells of this strain with the
desired recipient strain. The kurl-I strains are defective in nuclear fusion
From: Methods m Molecular Biology, Vol. 53 Yeast Protocols
Edited by: 1. Evans Humana Press Inc., Totowa, NJ
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