| Abstract: | Purified preparations of eucaryotic initiation factor 4B (eIF4B) from wheat germ bind the monocistronic, uncapped, mRNA satellite tobacco necrosis virus RNA (STNV RNA) in nitrocellulose-mediated binding assays. This reaction is mRNA specific and yields dissociation constants (Kd) in the 10(-7)-10(-8) M range, depending upon the particular enzyme preparation tested. Purified wheat germ eIF4A, in the presence or absence of ATP, does not bind STNV RNA efficiently, but added eIF4A and ATP do enhance the efficiency of the eIF4B-dependent binding of STNV RNA. Wheat germ eIF4B binds the oligonucleotide containing the 5'-terminal 52 nucleotides of STNV RNA (designated 1-52) with the same affinity as intact STNV RNA. This binding affinity is less with the 1-44 oligonucleotide of STNV RNA and does not occur with the 1-33 oligonucleotide of STNV RNA that contains the 5'-terminal untranslated region and the initiator AUG codon at positions 30-32 of this mRNA. Wheat germ eIF4B therefore binds the translation initiation region of STNV RNA, and this binding requires up to 20 nucleotides on the 3' side of the initiator AUG codon of this mRNA. Wheat germ eIF4B also efficiently binds an oligonucleotide containing nucleotides from positions 13-52 in from the 5' terminus of STNV RNA, thereby establishing that the postulated 5'-terminal stem and loop secondary structure of STNV RNA [Leung, D. W., Browning, K. S., Heckman, J. E., RajBhandary, U. L., & Clark, J. M., Jr. (1979) Biochemistry 18, 1361-1366] is not functional or essential for this specific binding reaction.(ABSTRACT TRUNCATED AT 250 WORDS) |
