Short interspersed repeats from Xenopus that contain multiple octamer motifs are related to known transposable...

We have identified in an intron of an X. laevis alpha-tubulin gene a member of a novel family of short (226-431 bp) interspersed repetitive elements. We have isolated other members of this family, which we term Ocr, from ovary cDNA and genome libraries and have identified another two in the published sequences of an H1B histone gene cluster and an actin gene intron. The termini of the Ocr elements are formed by a 19 bp inverted repeat that has clear sequence homologies to those of certain large transposable elements, such as 1723 (Xenopus) and Ac (maize). However, the Ocr elements do not appear to be deletion derivatives of larger transposons. The internal regions of the Ocr elements contain multiple copies of the octamer motif (ATTTGCAT) arranged as divergently-orientated dyads. We have shown by a gel mobility shift assay that these octamer dyads specifically bind what is presumably an OTF-type activator protein in oocyte nuclear extracts. We speculate that short interspersed repetitive families of this type may be generated by a mechanism of replicative transposition that uses a DNA intermediate and involves the interaction of DNA-binding proteins also utilised in other cellular processes.