PURIFICATION AND CHARACTERIZATION OF A NEW EUKARYOTIC PROTEIN TRANSLATION FACTOR - EUKARYOTIC INITIATION-FACTOR 4H

A new protein with translational activity has been identified on the b asis of its ability to stimulate translation in an in vitro globin syn thesis assay deficient in eukaryotic initiation factor (eIF) 4B and eI F4F, This protein has been purified to greater than 80% homogeneity fr om rabbit reticulocyte lysate and has been given the name eIF4H. eIF4H was shown to stimulate the in vitro activities of eIF4B and eIF4F in globin synthesis, as well as the in vitro RNA-dependent ATPase activit ies of eIF4A, eIF4B, and eIF4F, Three tryptic fragments of eIF4H yield ed amino acid sequences that were 100% identical to a human sequence f ound in the GeneBank(TM) that codes for a previously uncharacterized p rotein (HUMORFU_1). The calculated molecular weight of the protein enc oded by this sequence, its predicted cyanogen bromide fragmentation, a nd calculated isoelectric point are all consistent with those determin ed experimentally for eIF4H. Also, the presence of an RNA recognition motif within HUMORFU_1 suggests that eIF4H may interact with mRNA. We conclude that this newly characterized protein, eIF4H, functions to st imulate the initiation of protein synthesis at the level of mRNA utili zation, and is encoded by the gene for HUMORFU_1.