Bar to normal UGA translation by the selenocysteine tRNA

The selC gene product, tRNA(Sec), inserts selenocysteine at UGA (opal) codons in a specialized mRNA context. We have investigated the action of the tRNA at ordinary UGA codons, normally not translated, by changing the unusual structural features of tRNA(Sec). Sequences in the D arm, CCA arm and variable arm of the tRNA all contribute to the prohibition against translation of ordinary UGA codons. One multiple mutant is a moderately efficient serine-inserting UGA suppressor tRNA.