Opal suppressor serine tRNAs from bovine liver form phosphoseryl-tRNA

An unusual minor species of bovine liver serine tRNA has previously been isolated, sequenced, and found to suppress the UGA termination codon in protein synthesis in vitro [Diamond, A., Dudock, B. & Hatfield, D. (1981) Cell 25, 497-506]. We have now found that this tRNA can be a substrate in a specific phosphorylation reaction in which phosphoseryl-tRNA is formed. Moreover, bovine liver contains a second UGA suppressor serine tRNA (tRNASerNCA; N is a modified nucleoside) which also forms phosphoseryl-tRNA. The nucleotide sequence and coding properties of tRNASerNCA are presented.