Expression of fragments of translation initiation factor eIF4GI reveals a nuclear localisation signal within the N-terminal apoptotic cleavage fragment N-FAG.
The eukaryotic initiation factor eIF4GI plays a central role in the assembly of a competent initiation complex at the 5' end of an mRNA. Five isoforms of eIF4G exist in cells, arising from alternative translation initiation. During picornaviral infection or apoptosis, eIF4GI is cleaved proteolytically to yield distinct fragments. Using HeLa cells, we have examined the fate of these proteins in the cell. We have found that while endogenous eIF4GI is predominantly cytoplasmic, a population can also be visualised in the nucleus. Furthermore, eIF4GI is localised primarily at the nuclear periphery in the vicinity of eIF4E and PABP1. Transient transfection of HeLa cells with different myc-tagged isoforms of eIF4GI did not result in any obvious differences in their localisation. However, expression of discrete fragments of eIF4GI corresponding to those generated after apoptosis or picornaviral infection generated a distinctive, but intricate localisation pattern. Our work shows that the N-terminal apoptotic cleavage fragment N-FAG contains a sequence of basic amino acids that can act as a nuclear localisation signal. In addition, the presence or absence of the sequence flanking and including the eIF4E binding site (residues 533-682) confers a distinct cellular distribution pattern for the central domain of eIF4GI.
Coldwell
Mark J
MJ
School of Life Sciences, University of Sussex, Falmer, Brighton, BN1 9QG, UK.
Hashemzadeh-Bonehi
Lida
L
Hinton
Tracey M
TM
Morley
Simon J
SJ
Pain
Virginia M
VM
D000595:Amino Acid Sequence; D024361:Amino Acids, Basic; D017209:Apoptosis; D020169:Caspases / Q000378:metabolism; D002467:Cell Nucleus / Q000737:chemistry*; D039603:Eukaryotic Initiation Factor-4G; D016650:Fluorescein-5-isothiocyanate; D019085:Fluorescent Antibody Technique, Direct; D005456:Fluorescent Dyes; D017930:Genes, Reporter; D014644:Genetic Variation; D006367:HeLa Cells; D006801:Humans; D008856:Microscopy, Fluorescence; D009154:Mutation; D010442:Peptide Chain Initiation, Translational; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010448:Peptide Initiation Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010850:Picornaviridae Infections; D039122:Poly(A)-Binding Protein I / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary
D024361:Amino Acids, Basic; C113920:EIF4G1 protein, human; D039603:Eukaryotic Initiation Factor-4G; D005456:Fluorescent Dyes; D010446:Peptide Fragments; D010448:Peptide Initiation Factors; D039122:Poly(A)-Binding Protein I; D020033:Protein Isoforms; D020169:Caspases; D016650:Fluorescein-5-isothiocyanate