Repetitive sequences in Xenopus laevis

This thesis describes the characterization of two repetitive sequence families of the South African frog, Xenopus laevis. One family consists of repeated sequences 741 base pairs in length and the other family consists of repeated sequences 388 base pairs in length. Representative members of each family have been cloned. The structural organization of the sequence families was analyzed using the Southern blot technique. The 741 bp sequence was found to occur in tandem blocks of up to at least fourteen repeats. Sequence variants were found which have gained or lost the recognition sites for particular restriction enzymes. A DNA sequence approximately 1000 bp in length was found to have homology to the 741 bp sequence. Structural analysis of the 388 bp sequence revealed that it occurs in tandem blocks containing up to at least 12 repeats. Sequence variants occur within the population. This family was found to have a novel structural organization. The 388 bp sequence was found to occur in clusters with variable numbers of repeats; most of the clusters were found to have common flanking sequences. The X. laevis 388 bp sequence was found to have homology to a sequence of similar size found in two related species, X. boreal is and X. mulleri. The structural arrangement of these homologous families appears very similar to that found in X. laevis. The nucleotide sequences of the cloned 388 bp and 741 bp fragments were determined. The two sequences do not share obvious homology with each other. The sequences are not composed of simpler repeats. Potential open reading frames for short proteins were found in each sequence. Total RNA from X. laevis livers, embryos and oocytes was analyzed for the presence of homology to the cloned fragments. No evidence of stable transcripts of these sequences was found.