Hybridization of polyuridylic acid to human DNA immobilized onto nitrocellulose filters

The level of deoxyadenylate (da) regions in human DNA was estimated from formation of poly(U)-poly(da) triplexes on nitrocellulose filters that were RNAase resistant. The (dA) rich sequences were determined following mild ribonuclease treatment of the poly(U)-DNA hybrids (5 mug/ml at 25 degreesC for 30 min), where as exhaustive ribonuclease treatment (5 mug/ml at 25 degrees C for 6 hr) estimated the more (dA) pure sequences. The level of (dA) rich regions was 0.39% of the DNA and for the more (dA) pure regions it was 0.07%. The (dA) regions were widely distributed throughout human DNA regardless of base composition or sequence repetition. However, a concentration of (dA) regions into main band CsC1 gradient fractions of DNA and into repeated DNA was observed.