Abstract
This chapter focuses on ribonucleases that are involved in generating the 3' terminus of tRNA precursors and in cleaving a tRNA from a multicomponent transcript. Much of our knowledge about tRNA‐processing pathways has come from studies with Escherichia coli and bacteriophage‐infected E. coli, although there has been some examination of other bacteria as well. The major interest in E. coli is due primarily to the availability, in this system, of mutations that interfere with tRNA maturation, allowing processing intermediates to be identified and processing nucleases to be implicated in the processing pathway. However, the tRNA precursors isolated from these mutant strains have undergone partial processing. First, the tRNA portions of polycistronic precursors have been cleaved from the other RNAs with which they are co‐transcribed. Second, multimeric tRNA precursors generally have been converted to monomeric or dimeric forms. A major goal in the study of any metabolic pathway is to identify the enzymes that catalyze each of its reactions, to understand their specificity and mechanism of action, and to determine whether they are subject to regulation, either directly on their activity or on their synthesis. The chapter presents a summary of the exoribonucleases and endoribonucleases implicated in tRNA processing. Given the availability of mutant strains lacking many of these enzymes, alone or in combination, it is likely that the details of a tRNA processing pathway will be forthcoming in the near future.