title: The ATP-dependent interaction of eukaryotic initiation factors with mRNA.
abstract: The interaction of three protein synthesis initiation factors, eukaryotic initiation factor (eIF)-4A, -4B, and -4F, with mRNA has been examined. Three assays specifically designed to evaluate this interaction are RNA-dependent ATP hydrolysis, retention of mRNAs on nitrocellulose filters, and cross-linking to periodate-oxidized mRNAs. The ATPase activity of eIF-4A is only activated by RNA which is lacking in secondary structure, and the minimal size of an oligonucleotide capable of effecting an optimal activation is 12-18 bases. In the presence of ATP, eIF-4A is capable of binding mRNA. Consistent with the ATPase activity, this binding shows a definite preference for single-stranded RNA. In the absence of ATP, eIF-4F is the only factor to bind capped mRNAs, and this binding, unlike that of eIF-4A, is sensitive to m7GDP inhibition. The activities of both eIF-4A and eIF-4F are stimulated by eIF-4B, which seems to have no specific independent activity in our assays. Evidence from the cross-linking studies indicates that in the absence of ATP, only the 24,000-dalton polypeptide of eIF-4F binds to the 5' cap region of the mRNA. From the data presented in conjunction with the current literature, a suggested sequence of factor binding to mRNA is: eIF-4F is the first initiation factor to bind mRNA ind an ATP-independent fashion; eIF-4B then binds to eIF-4F, if in fact it was not already bound prior to mRNA binding; and finally, eIF-4A binds to the eIF-4F X eIF-4B X mRNA complex and functions in an ATP-dependent manner to allow unwinding of the mRNA.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D005914:Globins / Q000235:genetics; D007700:Kinetics; D010448:Peptide Initiation Factors / Q000378:metabolism*; D011131:Polyribonucleotides / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism
chemical_list: D010448:Peptide Initiation Factors; D011131:Polyribonucleotides; D012333:RNA, Messenger; D000255:Adenosine Triphosphate; D005914:Globins; D000251:Adenosine Triphosphatases