The Detection and Mapping of Point Mutations by RNase A Cleavage

Until recently, most defects identified in mutant genes have been based on large size differences, as detected by Southern or Northern blotting, or by the sequencing of cloned DNA fragments. However, it is probable that a large proportion of disease-causing mutations are point mutations. As a consequence of the rarity of RFLP markers showing linkage disequilibrium with mutant genes, and of point mutations that create or destroy restriction endo-nuclease recognition sites, it is of fundamental importance in medical molecular genetics to have a technique that will allow the direct detection of point mutations. Several techniques have been developed that go some way toward this goal: most notably, denaturing gradient gel electrophoresis (1 –3 ), Ribonuclease A (RNase A) cleavage (4 –6 ), and more recently, chemical cleavage (7 ,8 ).