Tandemly repeated DNA sequences from Xenopus laevis. II. Dispersed clusters of a 388 base-pair repeating unit

A repetitive DNA sequence family from Xenopus laevis that has an unusual genomic organization has been identified. It has been shown by blot-hybridization that this sequence occurs in clusters containing variable numbers of the 388 base-pair repeating unit. There are approximately 500 such clusters in the genome, and each cluster has common flanking sequences. The number of tandem 388 base-pair repeats per cluster ranges from one to at least 15, with a mean of seven. Homologous sequences were found in two related species, Xenopus borealis and Xenopus mulleri, where the size of the repeating units and their genomic arrangement are very similar to those in X. laevis. The complete nucleotide sequence of a cloned representative 388 base-pair repeating unit showed no short internal repeats and no long reading frames. By blot-hybridization, no evidence of transcripts of this sequence was found in total RNA from X. laevis liver, embryos or oocytes.