Endonucleolytically cleaves the 5'-leader sequence of certain mRNAs. Endonuclease digestion by the RNase J1/J2 complex occurs at a different site and in some cases more efficiently than J1 or J2 alone. The exonuclease activity of the J1/J2 complex is highly processive on substrates longer than 5 nucleotides, on shorter substrates is distributive. Plays a role in mRNA maturation and stability. Appears to have a limited effect on 16S rRNA maturation, despite its similarity to RNase J1. This subunit alone has very poor 5'-3' exonuclease activity. Binds 1 zinc ion per subunit. The inability to bind a second zinc ion may explain its very poor exonuclease activity (PubMed:21893285). kcat is 0.58 sec (-1) for J1, 0.13 sec (-1) for J1/J2 and <0.005 sec (-1) for J2. Unclear whether it forms homodimers or belongs to a larger complex. According to (PubMed:20025672) probably does not form homodimers, while (PubMed:21893285) shows homodimer formation. Both reports show RNase J1 and J2 interaction, probably as a heterotetramer (PubMed:19193632) shows it is a component of a possible RNA degradosome complex composed of rny, rnjA, rnjB, pnp, pfkA and eno, while (PubMed:20025672) finds no evidence of an RNA degradosome complex. Not essential. While depletion/deletion of RNase J1 or J2 has no large impact on global gene expression, a double mutant alters the expression of hundreds of genes (PubMed:18713320). Present in about 3000 monomers per cell in mid-log phase. Belongs to the metallo-beta-lactamase superfamily. RNA-metabolizing metallo-beta-lactamase-like family. Bacterial RNase J subfamily.