Splicing in Caenorhabditis elegans does not require an AG at the 3' splice acceptor site.
The dinucleotide AG, found at the 3' end of virtually all eukaryotic pre-mRNA introns, is thought to be essential for splicing. Reduction-of-function mutations in two Caenorhabditis elegans genes, the receptor tyrosine kinase gene let-23 and the collagen gene dpy-10, both alter the AG at the end of a short (ca. 50-nucleotide) intron to AA. The in vivo effects of these mutations were studied by sequencing polymerase chain reaction-amplified reverse-transcribed RNA isolated from the two mutants. As expected, we find transcripts that splice to a cryptic AG, skip an exon, and retain an unspliced intron. However, we also find significant levels of splicing at the mutated 3' splice site (AA) and at nearby non-AG dinucleotides. Our results indicate that for short C. elegans introns an AG is not required for splicing at either the correct 3' splice site or incorrect sites. Analysis of a splice site mutant involving a longer, 316-nucleotide C. elegans intron indicates that an AG is also not required there for splicing. We hypothesize that elements besides the invariant AG, e.g., an A-U-rich region, a UUUC motif, and/or a potential branch point sequence, are directing the selection of the 3' splice site and that in wild-type genes these elements cooperate so that proper splicing occurs.
Aroian
R V
RV
Howard Hughes Medical Institute, Pasadena, California.
Levy
A D
AD
Koga
M
M
Ohshima
Y
Y
Kramer
J M
JM
Sternberg
P W
PW
D000818:Animals; D001483:Base Sequence; D017173:Caenorhabditis elegans / Q000235:genetics*; D017238:Genes, Helminth; D007438:Introns; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D017354:Point Mutation; D012326:RNA Splicing; D012333:RNA, Messenger / Q000235:genetics
D009838:Oligodeoxyribonucleotides; D012333:RNA, Messenger