Abstract
Messenger ribonucleoprotein particles (mRNPs) have been isolated from rabbit reticulocyte polysomes. One of the proteins of the mRNP complex has many properties of a specific eukaryotic initiation factor, the soluble Met-tRNA-f binding protein. A purified preparation of this factor, in addition to binding Met-tRNA-f, binds poly(A) and globin mRNA. The binding of these substrates is greater than that obtained with other natural or artificial polyribonucleotides. The mRNP fraction also binds poly(A) and Met-tRNA-f. Since the factor which binds initiator tRNA also binds poly(A) and mRNA, and this activity can be found on mRNPs, there may be a relationship between initiator tRNA binding and messenger binding in early events of eukaryotic initiation.