Translation initiation factor 4A: a prototype member of dead-box protein family.

DEAD-box proteins are characterized by nine conserved helicase motifs. Several different DEAD-box proteins are found in eukaryotes, whereas prokaryotes have small number of these proteins. They play important roles in almost all kinds of RNA metabolism including roles in remodeling ribonuclear protein complexes. These proteins are usually very specific and cannot mutually be replaced. Many of these DEAD-box proteins (but not all) have been shown to have RNA-dependent ATPase and ATP-dependent RNA helicase activities. Many of them have also been shown to contain DNA unwinding activities. Translation initiation factor 4A is the prototype of the DEAD-box family of proteins. Actually, the DEAD-box protein family was discovered on the basis of conserved sequence motifs of eIF4A. Motif II (or Walker B motif) has the amino acids D-E-A-D (Asp-Glu-Ala-Asp), which gave the name to the family. In general, the eIF4A is considered as a helicase that locally melts the secondary structures and makes the RNA accessible to nucleases. It is part of the cap-binding complex eIF4F but is also found to be present in a free form. The biochemical activities of eIF4A are reported to be upregulated by eIF4B, eIF4H and eIF4G. It has been proposed that eIF4A helps to unwind secondary structures in the 5'-untranslated region, which are inhibitory for protein synthesis. In plants, it has been shown to play a unique role in abiotic stress tolerance, which suggests a new pathway to engineer to increase the crop production under the stress conditions.