Viral initiation of translation

Many viruses have evolved altrnative ways to initiate viral mRNA translation.The reason is either that the virus shuts off classic host translation, or because the viral RNAs are non-classical, missing a cap or polyadenylation.

Internal Ribosome Entry Site (IRES) are RNA structures that allow cap independent initiation of translation, and are able to initiate translation in the middle of a messenger RNA. Cripavirus IRES also allow the translation initiation on a Alanine or Glutamine tRNA.
Downstream Hairpin Loop (DLP) are RNA structures that allow initiation of cap dependent translation in the absence of eIF2 initiation factor, where the initiating methionine tRNA is placed by the DLP structure on the ribosome.
CUG initiation involves initiation with a leucine, and is more likely to occur upon stress with eIF2 inhibition .

Family Genus Type Species GROUP Initiation codon Host References
Dicistroviridae Cripavirus Cricket paralysis virus CrPV IRES Group I Alanine
Glutamine
Insects
Flaviviridae Hepacivirus Pestivirus Hepatitis C virus
Bovine diarrhea virus
Classical swine fever virus
IRES Group II Methionine Vertebrate
Nimaviridae Whispovirus White spot syndrome virus IRES Methionine Invertebrate
Picornaviridae Cardiovirus Aphtovirus Encephalomyocarditis virus
Foot and mouth disease virus
IRES Group III Methionine Vertebrate
Picornaviridae Enterovirus Hepatovirus Poliovirus
Hepatitis A virus
IRES Group IV Methionine Vertebrate
Polyomaviridae Polyomavirus SV40 IRES Methionine Vertebrate
Retroviridae Alpharetrovirus Rous sarcoma virus IRES Methionine Vertebrate
Betaretrovirus Mouse mammary tumor virus IRES Methionine Vertebrate
Gammaretrovirus Murine leukemia virus IRES Methionine Vertebrate
CUG Leucine Vertebrate
Deltaretrovirus Human T-lymphotropic virus IRES Methionine Vertebrate
Lentivirus Human immunodeficiency virus IRES Methionine Vertebrate
Togaviridae Alphavirus Sindbis virus DLP Methionine Vertebrate
Rubivirus Rubella virus DLP Methionine Vertebrate
Tombusviridae Carmovirus Pelargonium flower break virus IRES Methionine Plant
Totiviridae Giardiavirus Giardia lamblia virus IRES Methionine Protozoa