The rph-1 -Encoded Truncated RNase PH Protein Inhibits RNase P Maturation of Pre-tRNAs with Short Leader Sequences in the Absence of RppH

: RNase PH, encoded by the rph gene, is a 3'→5' exoribonuclease that in E. coli participates primarily in the 3' maturation of pre-tRNAs and the degradation of rRNA in stationary-phase cells. Interestingly, the routinely used laboratory strains of MG1655 and W3110 have naturally acquired the rph-1 allele, encoding a truncated catalytically inactive RNase PH protein which is widely assumed to be benign. Contrary to this assumption, we show that the rph-1-encoded Rph-1 protein inhibits RNase P-mediated 5'-end maturation of primary pre-tRNAs with leaders of <5 nucleotides in the absence of RppH, an RNA pyrophosphohydrolase. In contrast, RppH is not required for 5'-end maturation of endonucleolytically generated pre-tRNAs in the rph-1 strain and for any tRNAs in Δrph mutant or rph+ strains. We propose that the Rph-1 protein bound to the 3' end of the substrate creates a steric hindrance that in the presence of a triphosphate at the 5' end reduces the ability of RNase P to bind to the pre-tRNA.IMPORTANCE In this paper, we demonstrate that the rph-1 mutation found in commonly used E. coli strains leads to the synthesis of a truncated functionally inactive RNase PH protein that interferes with the 5'-end maturation of specific tRNAs with short 5' leaders by RNase P in the absence of RppH, an RNA pyrophosphohydrolase that converts primary 5' triphosphates into 5' monophosphates. The data presented indicate that the presence of the triphosphate interferes with RNase P binding to the pre-tRNA.