Functional characterization of five eIF4E isoforms in Caenorhabditis elegans.
Recognition of the 5'-cap structure of mRNA by eIF4E is a critical step in the recruitment of most mRNAs to the ribosome. In Caenorhabditis elegans, approximately 70% of mRNAs contain an unusual 2,2,7-trimethylguanosine cap structure as a result of trans-splicing onto the 5' end of the pre-mRNA. The characterization of three eIF4E isoforms in C. elegans (IFE-1, IFE-2, and IFE-3) was reported previously. The present study describes two more eIF4E isoforms expressed in C. elegans, IFE-4 and IFE-5. We analyzed the requirement of each isoform for viability by RNA interference. IFE-3, the most closely related to mammalian eIF4E-1, binds only 7-methylguanosine caps and is essential for viability. In contrast, three closely related isoforms (IFE-1, IFE-2, and IFE-5) bind 2,2, 7-trimethylguanosine caps and are partially redundant, but at least one functional isoform is required for viability. IFE-4, which binds only 7-methylguanosine caps, is most closely related to an unusual eIF4E isoform found in plants (nCBP) and mammals (4E-HP) and is not essential for viability in any combination of IFE knockout. ife-2, ife-3, ife-4, and ife-5 mRNAs are themselves trans-spliced to SL1 spliced leaders. ife-1 mRNA is trans-spliced to an SL2 leader, indicating that its gene resides in a downstream position of an operon.
Keiper
B D
BD
Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, Shreveport, Louisiana 71130-3932, USA.
Lamphear
B J
BJ
Deshpande
A M
AM
Jankowska-Anyszka
M
M
Aamodt
E J
EJ
Blumenthal
T
T
Rhoads
R E
RE
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D017173:Caenorhabditis elegans / Q000196:embryology / Q000235:genetics* / Q000502:physiology; D003001:Cloning, Molecular; D004625:Embryo, Nonmammalian / Q000502:physiology; D039561:Eukaryotic Initiation Factor-4E; D006801:Humans; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides; D010448:Peptide Initiation Factors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D010802:Phylogeny; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012315:RNA Caps / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D039561:Eukaryotic Initiation Factor-4E; D009838:Oligodeoxyribonucleotides; D010448:Peptide Initiation Factors; D020033:Protein Isoforms; D012315:RNA Caps; D011994:Recombinant Proteins