A novel family of retrotransposons in Xenopus with a developmentally regulated expression

We have obtained a novel family of LTR-retrotransposons in Xenopus laevis, named Xretpos, from cDNA and genomic clones. Its long terminal repeats (LTRs) can be subdivided into U3, R, and U3 to U5 region, and are bounded by 6 bp inverted repeats. Xretpos contains primer binding site and polypurine tract, and multiple copies of Xretpos-related element are present in the genome. A long open reading frame (ORF) encodes the CCHC motif conserved in retroviral gag proteins and leucine zipper motif capable of forming the coiled-coil. However, no amino acid homology to usually conserved retroviral pol gene was revealed. We report that in vitro synthesized Xretpos complementary RNAs are translated to produce a predicted size of protein. We also show that zygotically activated Xretpos transcripts are restricted to ventro-posterior specific regions and induced by UV-irradiation and BMP-4 overexpression in cycloheximide-dependent way. genesis 26:198-207, 2000.