Specific binding of Excherichia coli chain Initiation factor 2 to fMet-tRnafMet.

A stable Escherichia coli IF-2-fMet-tRNAfMet complex is formed upon incubation of IF-2 (prokaryotic initiation factor) with fMet-tRNAfMet is the presence of 50 mM Tris-HCl, pH 7.0, 100 mM NH4Cl, and 7 mM 2-mercaptoethanol. The complex thus formed is retained on a Millipore filter and is assayed accordingly. Complex formation does dot require GTP, is unstable in the presence of 5 mM Mg2+, and is specific for fMet-tRNAfMet. Other amino acyl-tRNAs or deacylated tRNAs do not form such a complex with IF-2. A crude ribosomal high salt wash preparation contains other protein factors which bind unspecifically to RNAs under the above binding conditions. One of these factors elute similarly to IF-1 on DEAE-cellulose chromatography. Extensively purified IF-1 and IF-3 show weak and unspecific RNA-binding activities. The RNA-protein complex formed in each of the above cases, like the IF-2-fMet-tRNAfMet complex, is retained on Millipore filter and is sensitive to Mg2+.