CONSTRUCTION AND CHARACTERIZATION OF A YEAST ARTIFICIAL CHROMOSOME LIBRARY CONTAINING 5 HAPLOID SUGAR-BEET (BETA-VULGARIS L) GENOME EQUIVALENTS

A yeast artificial chromosome (YAC) genomic library of Bera vulgaris w as constructed in the pYAC4 vector. High-molecular-weight DNA was prep ared from agarose-embedded leaf protoplasts from a triploid cultivar. The library was found to contain 33,500 clones in an ordered array of microtiter plates. Mean size of the inserts was estimated to be 135 kb , and the library should therefore represent the equivalent of five ha ploid genomes. The library was characterised for the presence of highl y repetitive, chloroplast and single-copy sequences. In order to isola te single-copy sequences, 18 pools of DNA, each from 1920 individual Y AC clones, were prepared for rapid screening of the library by the pol ymerase chain reaction. The results of these screenings showed that th e number of isolated clones was at or near the frequency expected.