Sequence organization and developmentally regulated transcription of a family of repetitive DNA sequences of Xenopus laevis.

Members of a family of DNA sequences of Xenopus laevis have been cloned and sequenced. Molecular analyses revealed that these sequences are moderately repetitive and dispersed throughout the genome. The sequences of seven clones were compared. Two of the clones lie in the globin gene cluster; one 5' to the adult alpha 1 gene, and the other in the first intron of the tadpole alpha 1 gene. In all clones, the homologous region begins at the same site, but the lengths of the common regions vary from 123 bp to over 320 bp due to heterogeneous 3' ends. Some of the repeats are bracketed by direct and/or inverted repeats, and relatively large palindromes were found 5' to the common region in some clones. These characteristics, and the presence of a repeat 5' to one of a pair of duplicated alpha genes suggests that some family members may be capable of transposition. A number of interesting features were found in the sequences, including multiple elements similar to the yeast autonomously replicating sequence, and a sequence which is about 80% homologous to the first 30 bases of the SV40 enhancer. Transcription studies revealed that homologous transcripts are detectable beginning at neurulation, increase in concentration up to stage 45, and disappear by metamorphosis. Implications of these data are discussed.