Alternative pre-mRNA splicing in Drosophila spliceosomal assembly factor RNP-4F during development.
The 5'- and 3'-UTR regions in pre-mRNAs play a variety of roles in controlling eukaryotic gene expression, including translational modulation. Here we report the results of a systematic study of alternative splicing in rnp-4f, which encodes a Drosophila spliceosomal assembly factor. We show that most of the nine introns are constitutively spliced, but several patterns of alternative splicing are observed in two pre-mRNA regions including the 5'-UTR. Intron V is shown to be of recent evolutionary origin and is infrequently spliced, resulting in generation of an in-frame stop codon and a predicted truncated protein lacking a nuclear localization signal, so that alternative splicing regulates its subcellular localization. Intron 0, located in the 5'-UTR, is subject to three different splicing decisions in D. melanogaster. Northern analysis of poly(A+) mRNAs reveals two differently sized rnp-4f mRNA isoforms in this species. A switch in relative isoform abundance occurs during mid-embryo stages, when the larger isoform becomes more abundant. This isoform is shown to represent intron 0 unspliced mRNA, whereas the smaller transcript represents the product of alternative splicing. Comparative genomic analysis predicts that intron 0 is present in diverse Drosophila species. Intron 0 splicing results in loss of an evolutionarily conserved stem-loop constituting a potential cis-regulatory element at the 3'-splice site. A model is proposed for the role of this element both in 5'-UTR alternative splicing decisions and in RNP-4F translational modulation. Preliminary evidences in support of our model are discussed.
Department of Zoology, Miami University, Oxford, OH 45056, USA.
Rebecca A
RA
Fetherson
Stephen B
SB
Strock
Kristen N
KN
White
Jack C
JC
Vaughn
D020121:5' Untranslated Regions; D017398:Alternative Splicing; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D004247:DNA; D004331:Drosophila melanogaster / Q000235:genetics*; D007438:Introns; D012322:RNA Precursors / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012261:Ribonucleoproteins / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid; D017381:Spliceosomes / Q000235:genetics*
D020121:5' Untranslated Regions; D012322:RNA Precursors; D012333:RNA, Messenger; D012261:Ribonucleoproteins; D004247:DNA