Master regulator of 5'-end-dependent mRNA decay (PubMed:18202662). Accelerates the degradation of transcripts by removing pyrophosphate from the 5'-end of triphosphorylated RNA, leading to a more labile monophosphorylated state that can stimulate subsequent ribonuclease cleavage (PubMed:18202662). Preferentially hydrolyzes diadenosine penta-phosphate with ATP as one of the reaction products (PubMed:11479323). Also able to hydrolyze diadenosine hexa- and tetra-phosphate (PubMed:11479323). Has no activity on diadenosine tri-phosphate, ADP-ribose, NADH and UDP-glucose (PubMed:11479323). In an RNase PH (rph) wild-type strain background, RppH is not required for maturation of tRNAs; however, strains with the truncated rph allele (for example K12 W1485 and its derivatives MG1655 and W3110) require RppH for maturation of certain monocistronic tRNAs with short (<5 nucleotides) leader sequences (PubMed:28808133). In the meningitis causing strain E.coli K1, has been shown to play a role in HBMEC (human brain microvascular endothelial cells) invasion in vitro (PubMed:10760174). Magnesium or zinc. Manganese can be used to a lesser extent. Optimum pH is 8.5-9.0. Monomer (PubMed:11479323). No interaction between this protein and catalytically inactive RNase PH was detected by immunoprecipitation (PubMed:28808133). Altered 5'-processing of primary pre-tRNA transcripts with short (<5 nucleotides) leaders; in the presence of the truncated inactive allele encoded by rph in strains derived from K12 W1485, including strains MG1655 and W3110 (PubMed:28808133). In the presence of wild-type (catalytically active) RNase PH no effect on processing (PubMed:28808133). No effect on growth rate, a slightly stronger effect is seen when combined with the inactive rph allele (PubMed:28808133). Belongs to the Nudix hydrolase family. RppH subfamily.