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

Summary 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.     

The dynamics of chromatin condensation: redistribution of topoisomerase II in the 87A7 heat shock locus during induction and recovery.

We have examined the in vivo sites of action for topoisomerases II in the 87A7 heat shock locus as a function of gene activity. When the hsp70 genes are induced, there is a dramatic redistribution of topoisomerase II in the locus which parallels many of the observed alterations in chromatin structure. In addition to changes in the topoisomerase II distribution within the locus, we find topoisomerase II localized around the putative domain boundaries scs and scs'. During recovery, when the chromatin fiber of the locus recondenses, the major sites of action for topoisomerase II appear to be located within the two hsp70 genes and in the intergenic spacer separating the two genes.     

Heat shock and developmental regulation of the Drosophila melanogaster hsp83 gene.

In contrast to the hsp70 gene, whose expression is normally at a very low level and increases by more than 2 orders of magnitude during heat shock, the hsp83 gene in Drosophila melanogaster is expressed at high levels during normal development and increases only severalfold in response to heat shock. Developmental expression of the hsp83 gene consists of a high level of tissue-general, basal expression and a very high level of expression in ovaries. We identified regions upstream of the hsp83 gene that were required for its developmental and heat shock-induced expression by assaying beta-galactosidase activity and mRNA levels in transgenic animals containing a series of 5' deletion and insertion mutations of an hsp83-lacZ fusion gene. Deletion of sequences upstream of the overlapping array of a previously defined heat shock consensus (HSC) sequence eliminated both forms of developmental expression of the hsp83 gene. As a result, the hsp83 gene with this deletion mutation was regulated like that of the hsp70 gene. Moreover, an in vivo polymer competition assay revealed that the overlapping HSC sequences of the hsp83 gene and the nonoverlapping HSC sequences of the hsp70 gene had similar affinities for the factor required for heat induction of the two heat shock genes. We discuss the functional similarity of hsp70 and hsp83 heat shock regulation in terms of a revised view of the heat shock-regulatory sequence.