Detection of a rare-cutter RFLP in a CpG-rich island near the cystic fibrosis locus

Abstract
The probe pCS. 7, isolated from an HpaII tiny fragments (HTF) island and tightly linked to the mutation causing cystic fibrosis (CF), detects a polymorphism with the rare-cutter restriction enzymeBssHII. In a single digest, the resulting restriction fragment length polymorphism (RFLP) cannot be detected by either conventional or pulse-field gel electrophoresis. A double digest withBssHII in conjunction with a six-cutter restriction enzyme that does not recognize a site containing a CpG dinucleotide enables the probe to be used routinely for prenatal diagnosis and carrier exclusion. This strategy can be used to identify polymorphisms in HTF islands.