SPECIFIC FUNCTION OF A G-CENTER-DOT-U WOBBLE PAIR FROM AN ADJACENT HELICAL SITE IN TRNA(ALA) DURING RECOGNITION BY ALANYL-TRANSFER-RNA SYNTHETASE

G . U wobble pairs are crucial to many examples of RNA-protein recogni tion. We previously concluded that the G . U wobble pair in the accept or helix of Escherichia coli alanine tRNA (tRNA(Ala)) is recognized in directly by alanyl-tRNA synthetase (AlaRS), although direct recognitio n may play some role. Our conclusion was based on the finding that amb er suppressor tRNA(Ala) with G . U shifted to an adjacent helical site retained substantial but incomplete Ala acceptor function in vivo. Ot her researchers concluded that only direct recognition is operative. W e report here a repeat of our original experiment using tRNA(Lys) inst ead of tRNA(Ala). We find, as in the original experiment, that a shift ed G . U confers Ala acceptor activity. Moreover, the modified tRNA(Ly s) was specific for Ala, corroborating our original conclusion and mak ing it more compelling.