Structural, functional and mechanistic analysis of the Bag-1 internal ribosome entry site

Bag-1 is an anti-apoptotic protein involved in the regulation of a number of cellular processes, notably as a co-chaperone for the 70kDa heat shock proteins. At least four protein products of Bag-1 have been isolated, p50, p46, p36 and a minor isoform, p29. The 5' UTR of the p36 isoform of Bag-1 has been shown to contain an internal ribosome entry segment (IRES). The internal ribosome entry mediated mechanism of translation has been shown to maintain Bag-1 expression when cap- dependent translation is compromised during heat shock. Many IRESes require trans-acting protein factors for optimal IRES activity. Bag-1 IRES activity is cell-type specific and is inefficient in cell lines with low endogenous levels of the /r