Translational control of the picornavirus phenotype

Picornaviruses are small animal viruses with positive-strand genomic RNA, w hich is translated using cap-independent internal translation initiation. T he key role in this is played by cis elements of the 5 ' -untranslated regi on (5 ' -UTR) and, in particular, by the internal ribosome entry site (IRES ). The function of translational cis elements requires both canonical trans lation initiation factors (eIFs) and additional IRES transacting factors (I TAFs). All known ITAFs are cell RNA-binding proteins which play a variety o f functions in noninfected cells. Specific features of translational cis el ements substantially affect the phenotype and, in particular, tissue tropis m and pathogenic properties of picornaviruses. It is clear that, in some ca ses, the molecular mechanism involved is a change in interactions between v iral cis elements and ITAFs. The properties and tissue distribution of ITAF s may determine the biological properties of other viruses that also use th e IRES-dependent translation initiation. Since this mechanism is also invol ved in translation of several cell mRNAs, ITAF may contribute to the regula tion of the most important aspects of the living activity in noninfected ce lls.