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Studies of Initiation Factors in Protein Synthesis of Host Liver and Transplantable Hepatoma¹

Department of Pathology, University of South Florida, College of Medicine, Tampa, Florida 33620

The activity of initiation factors obtained from host livers and transplantable H5123 hepatomas of Buffalo rats was investigated using an in vitro assay of protein synthesis. Initiation factors obtained by washing ribosomes with 1 M KC1, KC1-washed ribosomes, 60 S and 40 S ribosomal subunits, and transferases were prepared from liver and from tumor. The activity in polyuridylic acid [poly(U)]-directed polyphenylalanine synthesis and in the binding of phenylalanine-tRNA-¹⁴C and methionyl-tRNA-¹⁴C to 40 S ribosomal subunits at low Mg²⁺ concentrations was measured. Using a system requiring initiation factors, high-salt-washed ribosomes, transferases, and poly(U), initiation and subsequent synthesis of polyphenylalanine chains were found to increase when initiation factors from tumors were used in comparison to initiation factors from host livers. Studies on initiation factors-promoted binding of aminoacyl-tRNA's to 40 S small ribosomal subunits indicated that the initiation factors from tumor exhibited significantly greater activity in the formation of 40 S-phenylalanine-tRNA-poly(U) and 40 S-methionyl-tRNA-adenyluridylylguanosine complexes, than the initiation factors from host livers. The experiments also indicated that the initiation factors of tumor and liver could be interchanged in the test assay system. Initiation factors of hepatoma were able to stimulate polyphenylalanine synthesis and the binding of phenylalanine-tRNA and methionyl-tRNA to the same degree regardless whether the ribosomal species used were of host liver or of hepatoma. Studies also revealed that the activities of the ribosomes and transferases from host liver and tumor appeared to be similar.

¹ This investigation was supported by USPHS Research Grant CA-14156 from the National Cancer Institute.

Received 6/18/73. Accepted 10/29/73.