[Detection of tandem repeats in the genome of Citellus genus using restrictases]

DNA from ground squirrels of the Citellus genus (Rodentia, Sciuridae) were analysed by centrifugation in the presence of CsCl followed by digestion by restriction endonucleases. Digestion of DNA of two species C. undulatus and C. fulvus by 10 of the 16 restriction endonucleases used led to formation of electrophoretically discrete fragments that are multiple to 330 b.p. in length which points out the tandem organization of repetitive sequences similar to the satellite DNA of many mammal species. However, upon centrifugation we failed to reveal a satellite band in these species; hence the tandem repeats refer to the class of cryptic satellites in the ground squirrels and do not differ in base composition from the remaining part of DNA. The main fraction of the genome was revealed in the form of discrete fragments by cleavage with HindIII and AluI. Both of these restriction endonucleases were used for comparative analysis of DNA of 12 Citellus species. It has been shown that DNA of all species can be digested by HindIII and yields a series of fragments that are multiple to 330-30 b.p. in length and the total content of which varies from species to species within 4-22%. The fraction of the tandem repeats does not correlate with the systematic position of species nor with the amount of heterochromatin in the chromosomes. AluI cuts the DNA of 11 species yielding 110 and 220 b.p. fragments compared to only 60 and 280 b.p. in the DNA of C. dauricus. Under HindIII digestion we can also reveal the tandem repeats in marmot, which is phylogenetically close to the Citellus of the Marmota genus, but they have another periodicity--180 b.p. We propose that the age of ground squirrels repeats is 2-3 million years and they are significantly younger than the marmot repeats.