Maturation pathways for E. coli tRNA precursors: a random multienzyme process in vivo.

tRNA maturation consists of the specific removal of precursor sequences from both the 5' and 3' termini of an initial RNA transcript. How this is accomplished has heretofore not been ascertained in any system. Using Northern analysis of RNA isolated from a variety of RNase-deficient E. coli strains, we have identified the processing intermediates that accumulate in the absence of specific processing nucleases. From this information we have established the maturation pathways for 12 different E. coli tRNAs including the specific role of each of the relevant RNases in the process. The surprising conclusion from this work is that tRNA maturation is a stochastic process that lacks a defined order and that can proceed with a variety of alternative 3' processing nucleases.