Studies on the formation of transfer ribonucleic acid-ribosome complexes. VI. Oligopeptide synthesis and translocation on ribosomes in the presence and absence of soluble transfer factors.

Protein synthesis is the result of a series of coupled events, many of which can be measured. In this report, the determination of the synthesis of peptides of chain length three and greater was used as a measure of translocation, the movement of the ribosome along the polyribonucleotide template. Translocation was observed both in the presence and absence of one added soluble transfer factor with the use of a polyuridylic acid template; with the use of a polyadenylic acid template, translocation required the transfer factor (Factor G). Characteristics of oligophenylalanine formation in the presence and absence of Factor G suggested several conclusions. The lack of secondary structure of polyuridylic acid templates probably permits oligophenylalanine synthesis in the absence of any additional supernatant transfer factor. High magnesium ( >0.04 M) inhibits protein synthesis through its inhibition of translocation; this inhibition is independent of Factor G and therefore is an effect on the template-ribosome-transfer RNA complex. In contrast, the steroid antibiotic fusidic acid inhibits translocation through an effect on Factor G itself.