Isolation of a DNA sequence stimulating recombination in yeast

A series of DNA sequences was rescued from the yeast Saccharomyces cerevisiae transformed by a gene library and selected for the cdc35ts+, TRP1+ phenotype. These sequences did not complement the cdc35ts mutation, and were found in various amounts and orientations in degraded plasmids. A similar phenomenon was demonstrated when the HIS3 gene was cloned into one of them: a highly deleted plasmid was rescued from complemented homozygous diploid yeast cells, in which the HIS3+/his3- character was inherited at a 2:2 ratio. These results suggest that the insert sequences rescued from the cdc35ts transformants stimulate vigorous non-reciprocal recombination events by the transfer of HIS3 gene or the TRP-ARS fragment. This event was detected in the transformation of cdc35 or his3- hosts and was followed by the re-isolation of the degraded plasmid molecules.