A high degree of DNA strain polymorphism associated with the major heat shock gene in Caenorhabditis elegans.

We have searched for sequence variation between the Bristol and Bergerac strains of C. elegans in regions flanking three members of the 70 kilodalton (kd) heat shock peptide (hsp) gene family. No sequence variation was detected in 40 kb of DNA flanking two 70 kd hsp genes which are not stimulated by heat shock. In contrast, analysis of DNA flanking the heat shock inducible 70 kd hsp gene showed an unusually high amount of sequence variation between the two strains. Isolation and restriction map analysis of this gene from both strains revealed that the 5' and 3' flanking regions have diverged by 8.1 and 7.0% in nucleotide sequence, respectively. We have shown that these alterations are not due to large DNA rearrangements and conclude that the majority of sequence difference is the result of point mutations. Our results suggest that the heat shock inducible 70 kd hsp gene region accumulates mutations at a rate 10 to 20 fold higher than other regions of the genome. We propose that the anomalously high accumulation of mutational events is a direct consequence of the special status of the 70 kd hsp gene and its surrounding chromatin domain in the germline of C. elegans.