Translational control mechanisms spanning the beginning, middle, and end of the mRNA

The initiation of mRNA translation in eukaryotes is a highly regulated process that impacts on the study of oncology, virology, and molecular embryology. Translation requires several eukaryotic initiation factors (eIFs) that promote binding of ribosomes to the mRNA. Phosphorylation of eIF2, the factor that binds the initiator methionyl-tRNA, occurs in response to a variety of cell stresses, and results in inhibition of translation. The dsRNA-activated protein kinase PKR mediates phosphorylation of eIF2alpha upon viral infection, and possesses anti-viral and anti-proliferative properties. We studied the role of an insert sequence located between kinase subdomains IV and V of PKR, for both kinase activity and binding of the pseudosubstrate K3L from vaccinia virus. While deletion of the kinase insert sequence resulted in a loss of kinase activity, it was not required for K3L binding. The K3L binding site was identified between subdomains V and VI, which likely also corresponds to the eIF2 binding site. While PKR inhibits viral protein synthesis, the La autoantigen is a cellular protein that potentiates cap-dependent translation of human immunodeficiency virus (HIV), and cap-independent translation of poliovirus (PV) RNAs. Translation of both RNAs required the C-terminal portion of the La protein, which contains a dimerization domain. Addition of the dimerization domain caused a dose-dependent decrease in HIV and PV RNA translation in vitro, thus suggesting that La protein functions as a dimer during translation. Other regulators of translation include the 3' polyadenylate {poly(A)} tail of the mRNA and poly(A) binding protein (PABP). An interaction cloning approach was used to probe the function of PABP in mammalian cells, and a novel PABP-interacting protein (PAIP-1) was identified. PAIP-1 has homology to eIF4G and interacts with both PABP, and the RNA helicase eIF4A. Overexpression of PAIP-1 resulted in enhanced translation, possibly via bridging the 5' and 3' en