Stable tRNA precursors in HeLa cells

Two tRNA precursors were isolated from ³²P-labeled or unlabeled HeLa cells by two dimensional polyacrylamide gel electrophoresis and were sequenced. These were the precursors of tRNA^Met and tRNA^Leu, and both contained four extra nucleotides including 5′-triphosphates at their 5′-end and nine extra nucleotides including oligo U at their 3′-end. These RNAs are the first naturally occurring tRNA precursors from higher eukaryotes whose sequences have been determined. In these molecules, several modified nucleosides such as m²G, t⁶A and ac⁴C in mature tRNAs were undermodified. Two additional hydrogen bonds were formed in the clover leaf structures of these tRNA precursors. These extra hydrogen bonds may be responsible for the stabilities of these tRNA precursors.