U1 small nuclear RNA and spliceosomal introns in Euglenagracilis

U1 small nuclear RNA and spliceosomal introns in Euglenagracilis

Program in Evolutionary Biology, Canadian Institute for Advanced Research, Department of Biochemistry, Dalhousie University, Halifax, Nova Scotia B3H 4H7, Canada

Edited by Robert Haselkorn, The University of Chicago, Chicago, IL, and approved December 14, 1998 (received for review October 29, 1998)

Abstract

In the flagellated protozoon Euglena gracilis, characterized nuclear genes harbor atypical introns that usually are flanked by short repeats, adopt complex secondary structures in pre-mRNA, and do not obey the GT-AG rule of conventional cis-spliced introns. In the nuclear fibrillarin gene of E. gracilis, we have identified three spliceosomal-type introns that have GT-AG consensus borders. Furthermore, we have isolated a small RNA from E. gracilis and propose, on the basis of primary and secondary structure comparisons, that it is a homolog of U1 small nuclear RNA, an essential component of the cis-spliceosome in higher eukaryotes. Conserved sequences at the 5′ splice sites of the fibrillarin introns can potentially base pair with Euglena U1 small nuclear RNA. Our observations demonstrate that spliceosomal GT-AG cis-splicing occurs in Euglena, in addition to the nonconventional cis-splicing and spliced leader trans-splicing previously recognized in this early diverging unicellular eukaryote.

Footnotes

↵ * To whom reprint requests should be addressed. e-mail: M.W.Gray{at}Dal.Ca.
This paper was submitted directly (Track II) to the Proceedings Office.
Data deposition: The sequences reported in this paper have been deposited in the GenBank database [accession nos. U57366 (U1 snRNA) and AF102879 (fibrillarin genomic fragment/PCR product)].
ABBREVIATION:

snRNA,

small nuclear RNA;

RNP,

ribonucleoprotein;

SL,

spliced leader;

TMG,

N2,N2,7-trimethylguanosine