Protein–Precursor tRNA Contact Leads to Sequence-Specific Recognition of 5′ Leaders by Bacterial Ribonuclease P

Abstract

Bacterial ribonuclease P (RNase P) catalyzes the cleavage of 5′ leader sequences from precursor tRNAs (pre-tRNAs). Previously, all known substrate nucleotide specificities in this system are derived from RNA–RNA interactions with the RNase P RNA subunit. Here, we demonstrate that pre-tRNA binding affinities for Bacillus subtilis and Escherichia coli RNase P are enhanced by sequence-specific contacts between the fourth pre-tRNA nucleotide on the 5′ side of the cleavage site (N(−4)) and the RNase P protein (P protein) subunit. B. subtilis RNase P has a higher affinity for pre-tRNA with adenosine at N(−4), and this binding preference is amplified at physiological divalent ion concentrations. Measurements of pre-tRNA-containing adenosine analogs at N(−4) indicate that specificity arises from a combination of hydrogen bonding to the N6 exocyclic amine of adenosine and steric exclusion of the N2 amine of guanosine. Mutagenesis of B. subtilis P protein indicates that F20 and Y34 contribute to selectivity at N(−4). The hydroxyl group of Y34 enhances selectivity, likely by forming a hydrogen bond with the N(−4) nucleotide. The sequence preference of E. coli RNase P is diminished, showing a weak preference for adenosine and cytosine at N(−4), consistent with the substitution of Leu for Y34 in the E. coli P protein. This is the first identification of a sequence-specific contact between P protein and pre-tRNA that contributes to molecular recognition of RNase P. Additionally, sequence analyses reveal that a greater-than-expected fraction of pre-tRNAs from both E. coli and B. subtilis contains a nucleotide at N(−4) that enhances RNase P affinity. This observation suggests that specificity at N(−4) contributes to substrate recognition in vivo. Furthermore, bioinformatic analyses suggest that sequence-specific contacts between the protein subunit and the leader sequences of pre-tRNAs may be common in bacterial RNase P and may lead to species-specific substrate recognition.