Novel classes of mouse repeated DNAs

Abstract

Mouse DNA cleaved with Eco R11 (bst NI) displays two prominent restriction bands of 1.5 and 1.7 kb in agarose gels stained with ethidium bromide. These constitute novel subsets of repeated DNA in the mouse. Sequential Hoechst 33258-CsCl gradient fractionation of mouse DNA, yielding more GC rich main band DNA, and AT rich satellite DNA, revealed that both these fragments copurified with GC rich main band DNA. They were not detected in purified satellite preparations. Together these restriction bands constituted larger than or equal to 0.2% of main band DNAs. Hybridization of 32p labelled satellite DNA to blots of Eco R11 restricted mouse DNA showed positive hybridization only to smaller satellite restriction fragments, indicating satellite DNA had little or no homology with either the 1.5 or 1.7 kb fragments. The 1.5 and 1.7 kb fragments were isolated from gels and labelled with 32p by nick translation. Using a series of restriction endonucleases each of these two fragments showed different cleavage patterns. Filter hybridization confirmed that these two fragments were distinct subsets as they did not cross hybridize with each other. They also did not hybridize to other more minor repeated non-satellite DNA bands noted in ethidium bromide stained gels. Neither of them could be assigned to ribosomal genes as they did not hybridize to 32p kinase labelled 18S and 28S RNA. Isolation of DNA from male and female mice showed comparable amounts of both the 1.5 and 1.7 kb fragments. Thus neither was Y chromosome specific. From restriction patterns, and preliminary chromosome hybridization studies, these fragments are thought to represent "interspersed" repeated sequences rather than very long tandem (satellite like) centromeric arrays. The relationship between these repeated sequence subsets, their evolution and detailed organization, and their representation in different mouse species, remain to be determined.