In the mammalian genome CpG islands are associated with functional genes and cloning of these islands could be an alternative approach for cloning functional genes. Recently we have developed a new approach for cloning CpG islands and constructing NotI linking libraries. We have initiated the construction of a NotI restriction map for chromosome 3, especially focusing on the rearrangements in the 3p14-p21 region, which are associated with different malignancies. CpG islands from this region are useful for isolation of candidate tumor suppressor genes that map to this region and for isolating NotI-linking clones from 3p14-p21 for mapping purposes. Here we suggest a modification of Alu-PCR as an approach to isolating Not I sites (e.g., CpG islands) from defined regions of the chromosome. Instead of using whole chromosomal DNA for Alu-PCR, we have used representative NotI-linking libraries from hybrid cell lines containing either whole or deleted human chromosome 3 (MCH903.1 and MCH924.4, respectively). This decreases the complexity of the Alu-PCR products 10-100 times compared to the whole human genome. Using this modification, we can isolate NotI-linking clones, which are natural markers on the chromosome, rather than random genomic fragments. Among eight clones selected by this method, seven were from the region deleted in MCH924.4. The results clearly demonstrate the feasibility of Alu-PCR for isolating CpG islands from defined regions of the genome.
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