Before using any of the strains for mapping an unknown gene, check the strain with a known marker located on the specific chromosome for which the strain is being used. There have been reports of two incorrectly marked strains obtained from YGSC and from the Sherman-Wakem lab.
Mapping strains: chromosomal assignment with 2-micron tester strains (AB2)
Each of the 2-micron strains contains derivatives of the integrated plasmid YEp24 and is URA3+. It has become apparent that several of the 2-micron strains tend to lose the plasmid spontaneously at a rather high rate. To prolong stability of the integrated plasmid, revive the strains from paper replicas on Ura- medium rather than on rich YEPD medium. A study by Y. Kaneko of the Institute for Fermentation in Osaka, Japan, has established approximate percentages of loss of the Ura+ phenotype in the 2-micron strains when replica-plated from YEPD medium to Ura-. The results indicate that strains B-7588, B-7589, B-7175, B-7595, B-7596, B-7599, B-7602, B-7604, B-7608, B-7610, B-7612, and B-7614 become auxotrophic for uracil at a rate between 10 and 39%; the percentage loss of the Ura+ phenotype for all other strains is between 0.22 and 0.49%. For more precise numbers, please contact YGSC.