Abstract 1977 Poster Session II, Sunday, 5/2 (poster 187)

Autosomal dominant polycystic kidney disease (ADPKD) affects 1 out of 1,000 people and is one of the most common life threatening diseases. Over 85% of patients with ADPKD have mutations in the PKD1 gene. For the disease to manifest, a somatic mutation in the functional allele at the PKD1 locus appears to be required. We are interested in intrinsic and environmental factors that might facilitate this mutational process. The PKD1 gene contains the longest identified polypurine-polypyrimidine tract. We previously have shown that this sequence can adopt an array of intrastrand triple-helical structures. We wished to ascertain if this sequence was intrinsically unstable and if the mismatch repair system contributed to the instability as occurs in the triplet repeat mediated diseases. To test this hypothesis, we cloned the 2.5 kb polypurineapolypyrimidine tract from PKD1 into pBluescript. We propagated this plasmid for 200-30 generations in isogenic bacterial strains that identify effects of recombination, superhelical tension and DNA mismatch repair on mutagenesis. The significant, innate instability of the PKD1 intron 21 sequence is independent of recombination involving Rec A, and is not accentuated by increased negative superhelical tension. Bacterial strains deficient in mismatch repair proteins were equally prone to mutagenesis, this is in marked contrast to the instability in the triplet repeat mediated diseases. These findings support the hypothesis that the polypurine-polypyrimidine tract in intron 21 of the PKD1 gene is innately unstable, presumably by a different mechanism than triplet repeat sequences. We hypothesize that the ability of this sequence to form intrastrand triple-helical structures facilities this mutagenesis.

Research funded NIH grant KO8DK02418 and the Children's Hospital Research Foundation.