Interspersion of mouse satellite deoxyribonucleic acid sequences

Abstract

DNA sequences with homology to the major (A + T)-rich mouse satellite component were localized in CsCl gradients by hybridization with a labeled satellite c[complementary]RNA probe. Although, as expected, most of the hybridization was to DNA in the satellite-rich shoulder, substantial radioactive cRNA hybridized with DNA from denser regions of the gradient. Hybridization to main-band DNA was not due to physical trapping of satellite DNA in the gradient, and melting experiments argue that the associated radioactivity was due to true RNA/DNA hybridization. Nearest-neighbor analysis of hybridized [.alpha.-32P]CTP-labeled l-strand cRNA indicates that hybridization to main-band DNA is by the satellite cRNA and not a contaminant. Mouse satellite-like sequences apparently are interspersed within the main-band fraction of DNA. For the support of this contention, total mouse DNA, purified main-band DNA and purified satellite DNA were digested with EcoRI, sedimented in a sucrose gradient and hybridized with labeled satellite cRNA. Mouse satellite DNA is not cleaved with EcoRI, so that purified EcoRI-digested satellite DNA sediments as a high MW component. When total mouse DNA is digested with EcoRI, the majority of satellite-like sequences remain as high MW DNA; however, significant amounts of satellite-like sequences sediment with the bulk of the lower MW digested DNA, lending further credence to the argument that satellite-like sequences are interspersed with main-band DNA.