CONSTRUCTION OF A COMPLETE GENOMIC LIBRARY OF SACCHAROMYCES-CEREVISIAE AND PHYSICAL MAPPING OF CHROMOSOME-XI AT 3.7-KB RESOLUTION

A consortium of European laboratories has been organized to systematic ally sequence the genome of Saccharomyces cerevisiae. As part of the B IOTECH program aimed at sequencing chromosomes XI and II, we have cons tructed a total, genomic library of yeast strain FY1679 (a direct S288 C derivative) into cosmid vectors pWE15 and pOU61cos. Primary clones f rom four independent libraries totalling 190 genome equivalents have b een stored at -80 degrees C. A subset of 1939 independent clones (six genome equivalents) was hybridized using purified chromosomes XI and X as probes. A total of 147 chromosome XI-specific cosmid clones was us ed to construct the physical map of that chromosome. Mapping methods i ncluded a combination of classical bottom-up strategies (fingerprintin g, hybridizations) and a novel top-down strategy using I-SceI chromoso me fragmentation. The 147 cosmid clones form a unique contig covering the entire chromosome XI (666 kb) with the sole exceptions of the (C(1 -3)A)(n) repeats of the telomeres. Colinearity of cosmid inserts with yeast DNA was directly verified. A complete EcoRI map of chromosome XI was deduced from partial overlaps of cosmids and used for the sequenc ing program. Comparison of this map with the genetic map shows unexpec ted divergences that have been solved by subsequent genetic analysis, yet underline the necessity of independent physical mapping in genome projects.