| Satellite 2 DNA is a tandemly repeated, 330 bp sequence that is evolutionarily conserved among species belonging to the amphibian order, Caudata. Previous studies have shown that synthetic satellite 2 transcripts from the newt, Notophthalmus viridescens, self-cleave in vitro via a small structural motif called the hammerhead domain. Here we show that multimeric satellite 2 transcripts in the non-ovarian tissues of the newt self-cleave to generate monomeric satellite 2 transcripts. In contrast, monomeric transcripts in the newt ovary have ;By injecting cloned satellite 2 DNA into Xenopus oocytes, we determined that the satellite promoter is both structurally and functionally related to the small nuclear RNA (snRNA) gene promoters. Further comparison of satellite 2 DNA to the snRNA genes revealed that conserved core of the self-cleaving hammerhead domain resemble Boxes C and D found in several snRNAs. In addition, synthetic satellite 2 transcripts injected into Xenopus oocytes are immunoprecipitable by the anti-trimethylguanosine antibody, and endogenous nuclear satellite 2 transcripts in the newt oocyte possess the trimethylguanosine cap structure.;These data suggest that satellite 2 DNA is a member of the snRNA gene family. Accordingly, satellite 2 homologues are expected to exist in other vertebrate species. However, an extensive search in the genomes of non-Caudate amphibians such as Xenopus laevis has failed to detect the satellite 2 homologue. Based on our results, we propose that satellite 2 represents a Caudate-specific pseudogene family derived from an unidentified true snRNA gene. Apparently, significant sequence divergence between satellite 2 DNA and the putative progenitor gene have precluded the detection of the progenitor gene by standard hybridization methodologies using satellite 2 probes. |
