The importance of eIF4E2 (aka 4EHP in metazoan and nCBP in plants) in viral infection has been shown only indirectly in that modification of eIF4E2 by covalent addition of interferon-stimulated gene (ISG15) (ISGylation) results in binding to the 5'-cap with greater affinity than the unmodified protein (Okumura et al.
For example, viral protein covalently linked to the 5'-end of a plus-stranded viral genome can mimic the 5'-cap structure of host mRNA to recruit eIF4E, eIF4G, and/or eIF3 (Daughenbaugh et al.
(30) found that adding 5'-cap structures occurs early in HeLa hnRNA synthesis.
Nucleotide N in the 5'-cap [m.sup.7]GpppN(m) is the initiating nucleotide in gene transcription by PolII RNA polymerase.
The TOP motif is downstream of the 5'-cap of the mature mRNA and is present mainly in messengers encoding ribosomal proteins and elongation factors characteristic of protein synthesis (43).
In cells deficient in nutrients or growth factors, 4E BP1 binds to the eukaryotic initiation factor eIF4E preventing its binding to the 5'-cap mRNA or the initiation factor 4G (eIF4G).