THE DEAD BOX PROTEIN EIF4A - 2 - A CYCLE OF NUCLEOTIDE AND RNA-DEPENDENT CONFORMATIONAL-CHANGES

Limited proteolysis experiments have been carried out with the DEAD bo x protein eIF4A. The results suggest that there is a substantial confo rmational change in eIF4A upon binding single-stranded RNA, Binding of ADP induces conformational changes in the free enzyme and the enzyme. RNA complex, and binding of the ATP analogue AMP-PNP induces a conform ational change in the enzyme.RNA complex, The presence or absence of t he gamma-phosphate on the bound nucleotide acts as a switch, presumabl y via the Walker motifs, that mediates changes in protein conformation and, as described in the preceding paper in this issue: also mediates changes in RNA affinity. Thus, these results suggest that there is a series of changes in conformation and substrate affinity throughout th e ATP hydrolysis reaction cycle, A model is proposed in which eIF4A an d the eIF4A-like domains of the DEAD box proteins act as ATP-driven co nformational switches or motors that produce movements or structural r earrangements of attached protein domains or associated proteins, Thes e movements could then be used to rearrange RNA structures or RNA prot ein complexes.