Clustered and interspersed repetitive DNA sequences in four amphibian species with different genome size

Abstract

We have compared the amount of clustered and interspersed repetitive sequences in the genome of four Amphibia with different DNA contents per haploid nucleus: two Anura ( Xenopus laevis, 3 pg and Bufo bufo, 7 pg) and two Urodela ( Triturus cristatus, 23 pg and Necturus maculosus, 52 pg). High molecular weight DNA of the four species was denatured and reassociated to the same C 0 t in order to obtain duplex sequences with a similar reiteration frequency. Single-stranded DNA was digested off with the Aspergillus S 1 nuclease. DNA was then fractionated according to the molecular weight through an agarose A-50 column. We found that the amount of long repetitive sequences is roughly proportional to the genome size in the four species, while the number of short (about 300 base pairs) repetitive sequences is increased many-fold in the species with the larger DNA content, both in Anura and in Urodela.