Sequence and evolution of mouse satellite DNA

Abstract

A unique fragment of mouse satellite DNA has been isolated as a 240 base-pair insert in a lambda phage vector. Comparison of this “cloned” DNA fragment with total satellite DNA, by fingerprint analysis of their complementary RNA transcripts, indicates that the isolate possesses a characteristic mouse satellite sequence, with several oligonucleotides representing minor components subsumed in the diverged total satellite DNA. A linear sequence of the inserted DNA fragment has been obtained by primed DNA synthesis, from a fixed 5′ origin (a juncture between receptor and donor DNA) to specified 3′ nucleotides. This sequence, confirmed by alignment with overlapping cRNA oligonucleotides, gives some insight into the origins of mouse satellite DNA. An incomplete linear sequence has also been determined using total mouse satellite DNA, primed at the EcoRII restriction sites. The “average” sequence includes regions of high ambiguity, presumably due to divergence (sequence heterogeneity) and base methylation, but otherwise can be satisfactorily aligned with the cloned fragment sequence. The 240 base-pair repeat of total satellite is shown to be very homogeneous in length. This contrasts strikingly with the very irregular periodicity of component oligonucleotides, observed in the linear sequences. Moreover, there are no indications of intermediate periods of repetition in the sequence (between 15 and 70 base-pairs) as predicted by a model of successive doublings in the reiterated unit. The sequence obtained is consistent, however, with a two-stage model of satellite evolution through unequal recombination, or with a modified model of saltatory multiplication.