The invention provides a universal
yeast donor strain that contains a conditional
centromere and a URA3
allele on every
chromosome. This strain was constructed in four rounds of crosses of individual conditional
chromosome strains using a novel tetrad-based screen to identify segregants in which all marked chromosomes were contained in the same
spore. The invention also provides an improved high efficiency method to transfer extrachromosomal genetic material such as
plasmid DNA into any
Saccharomyces strain for use with the current
gene disruption libraries. The method of transfer is
mating-based method which uses a kar1
plasmid donor strain that can initiate
mating but cannot form a diploid and allows
plasmid transfer (plasmoduction) between nuclei in the heterokaryon. kar1 matings have been used to transfer YACs between
yeast strains, but previous methods required specialized genetic backgrounds in the recipient strains and suffered from high rates of spurious
chromosome transfer (Hugerat, Y., et al. 1994.
Genomics 22:108). Plasmoduction with the universal donor strain only requires that the recipient strain be ura3, GAL+ and have another marker available for selection of the transferred plasmid. Counterselection against every donor chromosome also limits the amount of spurious
allele transfer. The universal donor strain and the method of the invention are used to screen the
yeast gene disruption
library with plasmid-based
dominant negative alleles of various genes.