Construction of a library of bovine genomic fragments enriched in CpG islands

A procedure is described to isolate DNA probes from the bovine genome that are enriched in sites for the so-called rare cutter restriction endo- nucleases. A collection of Sac11(C"CGCGG)-Hin- dII1 fragments from bovine sperm was established in the plasmid Bluescript. 180 clones were picked at random and analysed for the presence of inserts with sites for the following rare cutters:EagI,BsshII,NarI,MluI,NruI,NaeI: 70%oftheclonescontainedatleast1siteand5% contained four different such sites. 22.8% had multiple sites for one or more of the rare cutters tested. Sequence analysis for 16 clones con- firmed the cloning of DNA with a G+C content and a proportion of CpG vs GpCs indicative of CpG islands.