(dA-dC)n.(dG-dT)n repeats mark the boundaries of a recent insertion event into a subgroup of Xenopus laevis hsp 30 gene promoters.

The Xenopus laevis hsp 30 gene family (encoding the 30-kDa heat shock proteins) consists of at least seven closely related members that are tandemly arranged in one or more clusters within the genome. This gene family appears to have been generated by a number of independent duplication events, each of which gave rise to one or more of the known members of the family. We report here the characterization of a genomic fragment that bears a high degree of similarity to a 192-bp region of the promoters of two hsp 30 genes (hsp 30A and hsp 30C) but not the promoters of any of the other hsp 30 genes isolated to date. The rest of this clone has no significant similarity to any other region of the hsp 30A and hsp 30C genes. It appears to represent a region of the genome that has undergone both duplication and subsequent insertion events fairly recently during the evolution of Xenopus laevis. Interestingly, the boundary regions of the insertion are marked by potential Z-DNA forming blocks of seven and nine perfect 5'-AC-3' dinucleotide repeats.