Short leader sequences may be transferred from small RNAs to pre-mature mRNAs by trans-splicing in Euglena.
Very closely related short sequences are present at the 5' end of cytoplasmic mRNAs in Euglena as evidenced by comparison of cDNA sequences and hybrid-arrested translation experiments. By cloning Euglena gracilis nuclear DNA and isolating the rbcS gene (encoding the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase), we have shown that the short leader sequence does not flank the nuclear gene sequence. The leader sequences were found to constitute the 5' extremities of a family of small RNAs. Sequencing six members of this family revealed a striking similarity to vertebrate U snRNAs. We propose that a trans-splicing mechanism transfers the spliced leader (SL) sequence from these small RNAs (SL RNAs) to pre-mature mRNAs. Transfer of leader sequences to mRNAs by trans-splicing has been shown only in trypanosomes where cis-splicing is unknown, and in nematodes where not more than 10% of the mRNAs have leader sequences. Our results strongly suggest that Euglena is a unique organism in which both a widespread trans-splicing and a cis-splicing mechanism co-exist.
Tessier
L H
LH
Institut de Biologie Moléculaire des Plantes du CNRS, Université Louis Pasteur, Strasbourg, France.
Keller
M
M
Chan
R L
RL
Fournier
R
R
Weil
J H
JH
Imbault
P
P
D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D016054:DNA, Protozoan / Q000235:genetics; D005055:Euglena / Q000235:genetics*; D008969:Molecular Sequence Data; D009693:Nucleic Acid Hybridization; D012326:RNA Splicing; D012333:RNA, Messenger / Q000378:metabolism*; D016053:RNA, Protozoan / Q000378:metabolism*; D012342:RNA, Small Nuclear / Q000378:metabolism*; D015183:Restriction Mapping; D012273:Ribulose-Bisphosphate Carboxylase / Q000235:genetics
D016054:DNA, Protozoan; D012333:RNA, Messenger; D016053:RNA, Protozoan; D012342:RNA, Small Nuclear; D012273:Ribulose-Bisphosphate Carboxylase