Expression of a X. laevis tRNATyr gene has been studied in mammalian cells. This tRNATyr gene has a 13 base intervening sequence adjacent to its anticodon. A fragment containing the tRNATyr gene was cloned into the late region of SV40. Cells infected with a recombinant virus stock vastly overproduce a tRNATyr that is properly spliced, processed and modified. It was also found that the X. laevis tRNATyr is identical or nearly identical to an endogenous tRNATyr of monkey kidney cells. The possibility of using the X. laevis tRNATyr gene to create an amber suppressor for mammalian cells is discussed.