Bacteriophage T3 and T7 early RNAs are translated by eukaryotic 80S ribosomes: active phage T3 coded S-adenosylmethionine cleaving enzyme is synthesized.

RNA transcribed in vitro from the early region of bacteriophage T3 or T7 was translated by cytoplasmic ribosomes which synthesized protein in cell-free systems prepared from mammalian cells and wheat germ. The proteins synthesized in vitro and their counterparts prepared from infected Escherichia coli comigrate by polyacrylamide gel electrophoresis with sodium dodecyl sulfate and are similarly affected by deletion or amber bacteriophage mutations. Bacteriophage T3 codes for an enzyme that cleaves S-adenosylmethionine and this activity was detected among the products of the mammalian cell-free system. Bacteriophage T3 or T7 RNA, after endoribonuclease III (EC 3.1.4.24) cleavage, gave higher levels of incorporation into phage T3 or T7 polypeptides than when an equivalent amount of the uncleaved RNA was added to the eukaryotic cell-free systems. Methylation of phage T3 or T7 RNAs is apparently not required for translation in either the wheat germ or mammalian cell-free system. The ability of T3 and T7 RNA to be translated in the presence of saturating amounts of natural eukaryotic mRNAs suggests that many prokaryotic genes introduced into mammalian cells might be expressed if they were transcribed in an appropriate form.