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J Biol Chem, Vol. 275, Issue 4, 2259-2264, January 28, 2000
The trans-Spliceosomal U4 RNA from the Monogenetic
Trypanosomatid Leptomonas collosoma
CLONING AND IDENTIFICATION OF A TRANSCRIBED tRNA-LIKE ELEMENT
THAT CONTROLS ITS EXPRESSION*
Liu
Li ,
Leo R.
Otake§,
Yu-xin
Xu¶, and
Shulamit
Michaeli
From the Faculty of Life Sciences, Bar-Ilan
University, Ramat-Gan 52900, Israel the § Department of
Molecular Biophysics and Biochemistry, Howard Hughes Medical Institute,
Yale University School of Medicine, New Haven,
Connecticut 06536-0812, and the ¶ Department of Biological
Chemistry, The Weizmann Institute of Science,
Rehovot 76100, Israel
U4 small nuclear RNA is essential for
trans-splicing. Here we report the cloning of U4 snRNA gene
from Leptomonas collosoma and analysis of elements
controlling its expression. The trypanosome U4 RNA is the smallest
known, it carries an Sm-like site, and has the potential for extensive
intermolecular base pairing with the U6 RNA. Sequence analysis of the
U4 locus indicates the presence of a tRNA-like element 86 base pairs
upstream of the gene that is divergently transcribed to yield a stable
small tRNA-like RNA. Two additional tRNA genes, tRNAPro and
tRNAGly, were found upstream of this element. By stable
expression of a tagged U4 RNA, we demonstrate that the tRNA-like gene,
but not the upstream tRNA genes, is essential for U4 expression and
that the B box but not the A Box of the tRNA-like gene is crucial for expression in vivo. Mapping the 2'-O-methyl
groups on U4 and U6 small nuclear RNAs suggests the presence of
modifications in canonical positions. However, the number of modified
nucleotides is fewer than in mammalian homologues. The U4 genomic
organization including both tRNA-like and tRNA genes may represent a
relic whereby trypanosomatids "hired" tRNA genes to provide
extragenic promoter elements. The close proximity of tRNA genes to the
tRNA-like molecule in the U4 locus further suggests that the tRNA-like
gene may have evolved from a tRNA member of this cluster.
*
This work was supported by German-Israeli Foundation Grant
I-353-078.03/94 and by National Institutes of Health Grant GM26154 (to
Joan A. Steitz).The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
The nucleotide sequence(s) reported in this paper has been submitted to the GenBankTM/EMBL Data Bank with accession number(s) AF204671.
¶
To correspondence should be addressed. Tel.: 972-3-531-8068;
Fax: 972-3-535-1824; E-mail: michaes@biu.mail.ac.il.
Copyright © 2000 by The American Society for Biochemistry and Molecular Biology, Inc.

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Copyright © 2000 by the American Society for Biochemistry and Molecular Biology.
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