Yx. Xu et al., THE U5 RNA OF TRYPANOSOMES DEVIATES FROM THE CANONICAL U5 RNA - THE LEPTOMONAS-COLLOSOMA U5 RNA AND ITS CODING GENE, Proceedings of the National Academy of Sciences of the United Statesof America, 94(16), 1997, pp. 8473-8478
Fractionation of the abundant small ribonucleoproteins (RNPs) of the t
rypanosomatid Leptomonas collosoma revealed the existence of a group o
f unidentified small RNPs that were shown to fractionate differently t
han the well-characterized trans-spliceosomal RNPs, One of these RNAs,
an 80-nt RNA, did not possess a trimethylguanosine (TMG) cap structur
e but did possess a 5' phosphate terminus and an invariant consensus U
5 snRNA loop 1, The gene coding for the RNA was cloned, and the coding
region showed 55% sequence identity to the recently described U5 homo
logue 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 subgr
oups 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. collosom
a homologue is longer (80 nt) and possesses a second stem-loop, Like t
he trypanosome U3, U6, and 7SL RNA genes, a tRNA gene coding for tRNA(
Cys) was found 98 nt upstream to the U5 gene, A potential for base pai
r interaction between U5 and SL RNA in the 5' splice site region (posi
tions -1 and +1) and downstream from it is proposed, The presence of a
US-like RNA in trypanosomes suggests that the most essential small nu
clear RNPs are ubiquitous for both cis- and trans-splicing, yet even a
mong the trypanosomatids the U5 RNA is highly divergent.