The majority of cellular stresses lead to the inhibition of cap-dependent t
ranslation, Some mRNAs, however, are translated by a cap-independent mechan
ism, mediated by ribosome binding to internal ribosome entry site (IRES) el
ements located in the 5' untranslated region. Interestingly, IRES elements
are found in the mRNAs of several survival factors, oncogenes and proteins
crucially involved in the control of apoptosis, These mRNAs are translated
under a variety of stress conditions, including hypoxia, serum deprivation,
irradiation and apoptosis. Thus, IRES-mediated translational control might
have evolved to regulate cellular responses in acute but transient stress
conditions that would otherwise lead to cell death.