title: A family of small nucleoplasmic RNAs with common structural features.
abstract: The four small nucleoplasmic RNAs designated as U1, U2, U4 and U5 RNA have a common structural domain or domain A. It is characterized by the presence of consensus sequence Pu-A-(U)5-G-Pup in a free single-stranded region and of the sequence Py-N-Py-Gp in the top loop of a hairpin located at the 3' end of the free region. Domain A is likely to be involved in a function common to the four small RNAs. Other domains possibly involved in the specific function of U1 and U5 RNAs are also presented. Several molecular forms of a same U RNA may be found in a same cellular type. These variant U RNAs are particularly numerous for U5 RNA. The possible origin of such new molecular forms is discussed in relation to multigene families for U RNAs. U1, U2, U4 and U5 RNAs are capped (with trimethylguanosine) and the consensus sequence for their 6 first nucleotides is A-(Py)5p. Thus, their 5' end resembles that of premessenger RNA, also capped (with monomethylguanosine) and bearing A-(Py)5p. Both classes of RNA are synthesized by RNA polymerase B, but the presence of a "TATA box" upstream of the capsite has not yet been demonstrated for U RNA genes. U1, U2, U4 and U5 RNAs bear a sequence C-Py-Pu at their 3' end or very close to it. This trinucleotide might be part of a site of post-transcriptional cleavage of U RNA precursors.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000818:Animals; D001483:Base Sequence; D002645:Chickens / Q000235:genetics; D004330:Drosophila / Q000235:genetics; D034441:Heterogeneous-Nuclear Ribonucleoproteins; D006801:Humans; D051379:Mice / Q000235:genetics; D009690:Nucleic Acid Conformation; D012313:RNA / Q000032:analysis* / Q000235:genetics / Q000502:physiology; D012315:RNA Caps / Q000032:analysis; D012326:RNA Splicing; D012342:RNA, Small Nuclear; D051381:Rats / Q000235:genetics; D012261:Ribonucleoproteins / Q000502:physiology; D017411:Ribonucleoproteins, Small Nuclear; D013045:Species Specificity; D014158:Transcription, Genetic; D014981:Xenopus / Q000235:genetics
chemical_list: D034441:Heterogeneous-Nuclear Ribonucleoproteins; D012315:RNA Caps; D012342:RNA, Small Nuclear; D012261:Ribonucleoproteins; D017411:Ribonucleoproteins, Small Nuclear; D012313:RNA