Characterization of a Xenopus laevis ribonucleoprotein endoribonuclease. Isolation of the RNA component and its expression during development.

In order to facilitate studies of the assembly and transport of the site-specific RNase mitochondrial RNA processing (MRP) ribonucleoprotein, we have characterized it from Xenopus laevis cells. X. laevis RNase MRP displayed a similar spectrum of cleavage activity to that produced by previously isolated mammalian nuclear enzymes. A 277-nucleotide RNA component of the ribonucleoprotein was identified; the gene for the RNA was isolated, sequenced, and found to be 66 and 63% similar to mouse and human RNase MRP RNAs, respectively. Despite the evolutionary distance from its mammalian counterparts, X. laevis RNase MRP RNA contains five regions of homology to the mammalian RNase MRP RNA. Four of these regions correspond to those previously identified as conserved between RNase MRP and RNase P RNAs; the fifth encompasses nucleotides recently discovered to be sufficient for autoantigen binding. The expression and assembly of Xenopus RNase MRP RNA were examined in frog oocytes and developing embryos. RNase MRP RNA was expressed throughout oogenesis; it started to accumulate at stage I and reached a maximum in stage IV. During embryogenesis RNase MRP RNA expression began to elevate at approximately stage 22 and continued to rise through the swimming tadpole stage. When injected into the nucleus of mature oocytes, the X. laevis RNase MRP RNA gene was expressed accurately, and transcripts were packaged into immunoprecipitable particles.