DOUBLET FREQUENCY-ANALYSIS OF FRACTIONATED VERTEBRATE NUCLEAR-DNA

Various sub-fractions of vertebrate [Cricetulus griesus, Chinese hamster; Cavia porcellus, guinea-pig; Mus musculus, mouse; Xenopus laevis] nuclear DNA were isolated and examined for sequence-dependent characteristics by nearest neighbor base-sequence (doublet) analysis. These include density, renaturation rate, satellite, chromatin and ribosomal cistron DNA fractions. The results of the analyses were compared together with sequence properties of 5S RNA and tRNA, in order to establish degrees of relationship. All sub-fractions showed very similar patterns of deviation from random expectation (general designs) except those fractions which on theoretical grounds are expected not to be directly involved in coding for polypeptides (satellite DNA, ribosomal cistron DNA, DNA coding for 5S RNA and tRNA). These findings are considered in relation to the still limited information available for mammalian mRNA sequences and to the doublet frequency properties of the DNA of small genome viruses of mammals. It is concluded that the highly characteristic general design of bulk n[nuclear]DNA, and of the majority of individual sub-fractions of nDNA, is shared by those fractions of nDNA that code for proteins which in turn implies that they have all evolved in response to the same major selection pressures.