Interaction of a selenocysteine-incorporating tRNA with elongation factor Tu fromE.coli

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Abstract
Selenocysteine-incorporating tRNASec(UCA), the product of selC, was isolated from E.coli and aminoacylated with serine. The equilibrium dissociation constant for the interaction of Ser- tRNASec(UCA) with elongation factor Tu GTP was determined to be 5.0±2.5×10−8 M. Compared with the dissociation constants of the two elongator Ser-tRNASer species (Kd = 7 × 10−10 M), the selenocysteine-incorporating UGA suppressor tRNA has an almost hundred fold weaker affinity for EF-Tu·GTP. This suggests a mechanism by which the Ser-tRNASec is prevented in recognition of UGA codons. This tRNA is not bound to EF-Tu·GTP and is converted to selenocysteinyl-tRNASec. We also demonstrate the lack of an efficient interaction of Sec with EF-Tu·GTP. The results of this work are in support of a mechanism by which the selenocysteine incorporation at UGA nonsense codons is mediated by an elongation factor other than EF-Tu·GTP.