摘要：

Escherichia coli restriction enzyme II breaks mouse satellite DNA into fragments which form a series of bands on gel electrophoresis. The DNA in the strongest band has a length of 220 to 260 nucleotide pairs and the other bands are multiples of this length. It is shown that these fragments are linked together in long arrays in the satellite sequence. The reassociation register of the DNA is about half the length of the 220 to 260 nucleotide pair fragment. In the electrophoresis pattern of the Eco RII † † Abbreviations used: Eco RII, restriction endonuclease from E. coli fi − (RII); Hae III, restriction endonuclease from Haemophilus aegyptius; Hind, restriction endonuclease from Haemophilus influenzae d. fragments other weaker bands can be seen. The stronger bands of the minor patterns fall half-way between the bands of the main pattern and the smallest is 120 to 130 nucleotide pairs long. The properties of the minor fragments suggest short spacings of the restriction site which have been produced by unequal crossing-over. The extents of divergence and unequal crossing-over are estimated. From this analysis and the sequence analysis described in the accompanying paper (Biro et al., 1975) it is proposed that mouse satellite DNA consists of an hierarchy of four periodicities which reflect stages in the evolution of the sequence. Digestion of mouse satellite DNA with Hae III produces fragments with the same sizes as those produced by Eco RII, but the yields are much lower. It is suggested that Hae III sites have been introduced by divergence and subsequently spread by unequal crossing-over.

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