Mapping Cloned Sequences on YACs

The mapping of a large number of cloned sequences on yeast artificial chromosome (YAC) clones 1s a srgmficant technical challenge. Although yeast colony lifts are suitable for hybridizations with a limited number of probes, this approach can be difficult to scale up to accommodate hundreds or thousands of probes. We have developed a strategy to map Arabidopsis thaliana expressed sequence tags (EST) to YACs, which 1s entirely based on the use of the polymerase chain reaction (PCR) to amplify specific plant genomic sequences. Although we are using these methods to map ESTs (1 ,2 ), the same approach can be used to map any sequence onto YAC clones.