Genes and pseudogenes for mouse U1 and U2 small nuclear RNAs.

Regions of the mouse genome homologous to U1 and U2 small nuclear RNAs have been isolated. The U1 regions are identified as pseudogenes on the basis of: 1) insertions, deletions, and substitutions in the sequence of the DNA as compared with that of U1 RNA; 2) absence of complementary RNA in mouse tissues; and 3) lack of expression upon microinjection in Xenopus oocyte nuclei. A U2 region is identified as a gene on the basis of near identity of sequence with U2 RNA and capacity to direct the synthesis of U2-like RNA in Xenopus oocyte nuclei. Both U1 and U2 sequences are repeated in the mouse genome, the U2 sequences analyzed here in an inverted repeat arrangement.