Proximity of polyriboguanylic acid-reactive sites in mammalian DNA to portions of DNA preferentially hybridizing with cellular RNA.

Transcribed portions of mouse nuclear DNA are adjacent to sites reacting preferentially with polyriboguanylic acid [poly(G)]. This spatial relationship was suggested by hybridization of radioactively labeled Ehrlich ascites RNA with denatured mouse DNA, the latter fractionated by centrifugation in CsCl equilibrium density gradients both in the presence and in the absence of various synthetic polyribonucleotides. The fractions of DNA which preferentially reacted with guanylic acid-rich polyribonucleotides hybridized with radioactive RNA to a higher degree than did the bulk of cellular DNA. This ability to react with polyriboguanylic acid-containing polymers was further enhanced by breaking DNA by sonication. No increased tendency for such hybridization was seen with the DNA that preferentially reacted with polyribouridylic acid.