Instability in the human genome

The DNA flanking hypervariable minisatellite MS32 was sequenced and searched for polymorphisms. The polymorphisms found were used in recombination analysis by A.J. Jefferys which described the recombination hotspot immediately flanking MS32, and responsible for the polarity of mutation observed within the repeat array. It became apparent that gene conversion and crossover processes at the locus were probably initiated in the same manner. Comparative analysis of the sequence flanking MS32, MS31 and CEB1 revealed all were situated in an environment rich in dispersed repeats and other repetitive DNA. Other minisatellites are not clustered near MS32, probably reflecting its interstitial location. Evidence suggested the existence of two diverged genes flanking CEB1. No candidates for a conserved sequence element acting as a cis-acting mutation initiator were found. No unusual conserved secondary DNA structures were found. No apparent association between base composition and hypervariability was found. Double-stand breaks which might play a role as recombination intermediates were detectable in DNA prepared from human testis tissue, but the possibility that they were artifacts could not be eliminated. Gel shift assays identified a complex, partly double-strand specific binding activity with preference for sequence including the OIG/C polymorphism which is associated with variations in the mutation rate at the minisatellite MS32; but it proved extremely difficult to purify for further analysis.