eIF4A: the godfather of the DEAD box helicases

Abstract

eIF4A has long been considered the "gold standard" for DEAD box helicases. In large measure, this reflected two items: first, the role of eIF4A in protein synthesis initiation was relatively well established. Second, a wide variety of biochemical studies had established the ability of eIF4A to bind nucleic acids in an ATP-dependent manner, to hydrolyze ATP in an RNA-dependent manner, and to unwind RNA duplexes in an ATP-dependent manner. In this article, these basic observations are reviewed for biochemical consistency and also interpreted in light of the available crystal structures for DEAD box proteins. The role of non-processive vs. processive helicase activity in protein synthesis is discussed. Also examined is the influence of ancillary protein factors (eIF4B, eIF4G, and eIF4H) on this activity. Finally, the "real" role(s) for eIF4A helicase activity in protein synthesis is discussed and related to other circumstances that likely also involve the use of non-processive or slightly processive DEAD box helicases (ribosome biosynthesis, RNA splicing).