Rapid screening of a YAC library by pulsed-field gel Southern blot analysis of pooled YAC clones.

A new method for screening of YAC libraries is described. Individual YACs were pooled into groups of 384 clones and prepared as samples suitable for pulsed-field gel electrophoresis. A five hit human YAC library (Brownstein et al., 1989) containing approximately 60,000 clones was condensed into 150 such pools and chromosomal DNAs in each sample were separated on three pulsed field gels containing 50 samples each. Southern blots prepared from these gels were hybridized with probes of interest to identify pools containing homologous YACs. Further purification was performed using standard colony hybridization procedures. Twenty-one probes used thus far have identified 47 positive pools and corresponding YACs have been purified from 28 of these. Some significant advantages of this method include avoidance of DNA sequence analysis and primer generation prior to YAC screening and the ability to handle the entire library on three filters. The screening approach described here permits rapid isolation of YACs corresponding to unsequenced loci and will accelerate establishment of YAC contigs for large chromosomal segments.