Cleavage of tRNA precursors by the RNA subunit of E. coli ribonuclease P (M1 RNA) is influenced by 3'-proximal CCA in the substrates.

tRNA precursor molecules that contain the CCA sequence found at the 3' termini of all mature tRNAs are cleaved in vitro more readily by M1 RNA, the catalytic subunit of E. coli RNAase P, than precursors that lack this sequence. The sensitivity to the CCA sequence is not apparent when precursors are cleaved by the reconstituted RNAase P holoenzyme that contains both M1 RNA and the protein subunit. These results have been obtained with monomeric precursor molecules encoded by the E. coli and human chromosomes and with three dimeric precursor molecules encoded by the bacteriophage T4 genome. The data are in agreement with previous results concerning T4 tRNA biosynthesis in vivo and show that the CCA sequence is important for the processing of precursors to tRNAs.