The U5 RNA of trypanosomes deviates from the canonical U5 RNA: the Leptomonas collosoma U5 RNA and its coding gene.
Fractionation of the abundant small ribonucleoproteins (RNPs) of the trypanosomatid Leptomonas collosoma revealed the existence of a group of unidentified small RNPs that were shown to fractionate differently than the well-characterized trans-spliceosomal RNPs. One of these RNAs, an 80-nt RNA, did not possess a trimethylguanosine (TMG) cap structure but did possess a 5' phosphate terminus and an invariant consensus U5 snRNA loop 1. The gene coding for the RNA was cloned, and the coding region showed 55% sequence identity to the recently described U5 homologue of Trypanosoma brucei [Dungan, J. D., Watkins, K. P. & Agabian, N. (1996) EMBO J. 15, 4016-4029]. The L. collosoma U5 homologue exists in multiple forms of RNP complexes, a 10S monoparticle, and two subgroups of 18S particles that either contain or lack the U4 and U6 small nuclear RNAs, suggesting the existence of a U4/U6.U5 tri-small nuclear RNP complex. In contrast to T. brucei U5 RNA (62 nt), the L. collosoma homologue is longer (80 nt) and possesses a second stem-loop. Like the trypanosome U3, U6, and 7SL RNA genes, a tRNA gene coding for tRNACys was found 98 nt upstream to the U5 gene. A potential for base pair interaction between U5 and SL RNA in the 5' splice site region (positions -1 and +1) and downstream from it is proposed. The presence of a U5-like RNA in trypanosomes suggests that the most essential small nuclear RNPs are ubiquitous for both cis- and trans-splicing, yet even among the trypanosomatids the U5 RNA is highly divergent.
Xu
Y x
Yx
Department of Membrane Research and Biophysics, The Weizmann Institute of Science, Rehovot 76100, Israel.
Ben-Shlomo
H
H
Michaeli
S
S
D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D017125:Genes, Protozoan; D008969:Molecular Sequence Data; D012326:RNA Splicing; D016053:RNA, Protozoan / Q000235:genetics*; D012342:RNA, Small Nuclear / Q000235:genetics*; D017421:Sequence Analysis; D014351:Trypanosomatina / Q000235:genetics*
D016053:RNA, Protozoan; D012342:RNA, Small Nuclear