Most eukaryotic mRNAs depend upon precise removal of introns by the spliceosome, a complex of RNAs and proteins. Splicing of pre-mRNA is known to take place in Dictyostelium discoideum, and we previously isolated the U2 spliceosomal RNA experimentally. In this study, we identified the remaining major spliceosomal RNAs in Dictyostelium by a bioinformatical approach. Expression was verified from 17 small nuclear RNA (snRNA) genes. All these genes are preceded by a putative noncoding RNA gene promoter. Immunoprecipitation showed that snRNAs U1, U2, U4, and U5, but not U6, carry the conserved trimethylated 5 cap structure. A number of divergent U2 species are expressed in Dictyostelium. These RNAs carry the U2 RNA hallmark sequence and structure motifs but have an additional predicted stem-loop structure at the 5 end. Surprisingly, and in contrast to the other spliceosomal RNAs in this study, the new U2 variants were enriched in the cytoplasm and were developmentally regulated. Furthermore, all of the snRNAs could also be detected as polyadenylated species, and polyadenylated U1 RNA was demonstrated to be located in the cytoplasm.Removal of introns by splicing is an essential step in the maturation of most eukaryotic mRNAs. This reaction is carried out by the spliceosome, a complex of the spliceosomal small nuclear RNAs (snRNAs) U1, U2, U4, U5, and U6 and their associated proteins. The spliceosomal RNAs interact with each other and the pre-mRNA by base pairing, thus keeping the pre-mRNA-spliceosome complex in position for the splicing reaction to occur (for reviews, see references 46 and 63). Most likely, the snRNAs are also responsible for the catalysis of the reaction (52).The U1, U2, U4, and U5 snRNAs are transcribed by RNA polymerase II and acquire a monomethylated 5Ј cap structure (m 7 G) in the nucleus (for reviews of small nuclear ribonucleoprotein [snRNP] biogenesis and snRNA modifications, see references 34 and 58). Following transport to the cytoplasm, the snRNAs are subjected to further maturation. Here, the 5Ј cap is trimethylated (m 2,2,7 G), and specific proteins are assembled upon the different snRNAs to form snRNPs, which are then transported back into the nucleus. The biogenesis pathway of U6 snRNA is different in that this RNA is transcribed by RNA polymerase III, the 5Ј-end triphosphate is ␥-monomethylated, and the RNA is thought never to leave the nucleus (58).During the past few years, polyadenylation of noncoding RNA (ncRNA) such as snRNA, small nucleolar RNA (snoRNA), and rRNA has been observed in budding yeast strains lacking the nuclear exosome component Rrp6 (2, 27, 54). Historically, polyadenylation in eukaryotes has been regarded as a phenomenon restricted to mRNA, where it has been demonstrated to be coupled to nuclear export, mRNA stabilization, and increased translation efficiency (reviewed in references 8 and 57). For prokaryotes, on the other hand, polyadenylation of both ncRNA and mRNA has been shown to promote RNA degradation (for a review, see reference 11). A number of recent stu...