Figure 7.

Model for La engagement of folded versus unfolded pre-tRNAs. (A) The RNA chaperone La preferentially engages pre-tRNAs via their UUU-3′OH containing trailers (18,22,23,55) as well as through contacts to the main body of the pre-tRNA (8,13), but without discriminating folded from misfolded pre-tRNA substrates (this work). (B) During the window of La occupancy, misfolded pre-tRNAs acquire the native fold through post-transcriptional modification by Trm1 (30,36) and/or La RNA chaperone activity (8,12–14,16,29). La affinity for the pre-tRNA does not change as the native fold is acquired. Thus this window benefits the misfolded pre-tRNA but not the pre-tRNA that did not benefit from La dependent rescue. (C) La remains with the pre-tRNA until trailer cleavage and La dissociation (13,18).