Resolution and characterization of polymorphic DNA by SSCP and chemical cleavage methodologies

A variety of techniques have been developed to detect single-base changes for the two different purposes. One is the detection of mutational events without phenotypic selection, and another is the rapid and conventional identification of mutations such as the specific base changes related to activation of oncogene, genetic diseases, etc. In this study, the utility of the two methods, single strand conformation polymorphism (SSCP) and chemical cleavage, was explored using 13 E. coli lacI- mutations cloned onto M13 phase. The 167 base region encompassing mutations was amplified by PCR as dsDNA. Following denaturation, these PCR products were analyzed by non-denaturing polyacrylamide gel electrophoresis (SSCP) and the separation of the ssDNA fragment carrying the altered sequence from the original sequence was found to be dependent on the location and type of the change. Hetero duplexes of changed/original sequences were also prepared by hybridization of the above PCR products. Mismatched C and T bases were modified by hydroxylamine and osmium tetroxide, respectively, and subsequently treated with piperidine to analyze the cleaved DNA fragments on a polyacrylamide gel (Chemical Cleavage). The cleavage efficiency was also found to be influenced by the type of mismatch and its surrounding sequence. Such observed characteristics should contribute to a better appreciation for these types of mutational systems, which in turn should lead to insight into the mechanisms of mutagenesis.