A FAMILY OF CENTROMERIC SATELLITE DNAS FROM THE EUROPEAN BROWN FROG RANA-GRAECA-ITALICA

Digestion of Rana graeca italica DNA with Asp718I produces highly repe titive fragments of 281 and 385 bp that were cloned and sequenced. The shorter fragment corresponds to the unit repeat (RgiS1b) of a satelli te DNA. The longer fragment was found to be part of a 494-bp repeat of another satellite DNA (RgiS1a) that was cloned intact as an EcoRV fra gment. RgiS1b is 97% homologous to RgiS1a, from which it seems to be d erived by a single deletion. Among all species tested, only the relate d brown frog Rana dalmatina contained homologous repetitive DNA. The o verall number of RgiS1a and RgiS1b repeats per R. graeca italica haplo id genome was estimated to be 2.7 x 10(5). RgiS1a and RgiS1b repeats a re organized in separate arrays, but repetitive units formed by variou s combinations of the two repeats were also observed on Southern blots . The amount of these extra repeats varies greatly among animals from the same population, representing a rare case of individual variabilit y in the satellite DNA organization. FISH with probes specific for bot h satellites, or for RgiS1a only, labeled the centromeric and pericent romeric heterochromatin of all chromosomes. This indicated that RgiS1a and RgiS1b are interspersed within the same heterochromatic regions o f the chromosomes.