Toxic component of a type VII toxin-antitoxin (TA) system. Upon cloning in E.coli inhibits cell growth for several hours; eventually cells recover and start growing. Cleaves the last 4 nucleotides from the tRNA acceptor stem (shown in vitro with E.coli tRNA-Glu(UUC)); only cleaves intact tRNA. Has no activity on mRNA. Neutralized by coexpression with cognate antitoxin MntA, which is due to di-AMPylation of the RNase. (tRNA)-3'-end (ribonucleoside 5'-phosphate)-(guanosyl 5'-phosphate)-(cytosyl 5'-phosphate)-(cytosyl 5'-phosphate)-(adenosine 5'-phosphate) + H2O = GpCpCpA + H(+) + tRNA 3'-end (ribonucleotide 3'-phosphate) Homodimer. Forms a complex with MntA, probably MntA(1):HepT(2) in vivo; can only be purified when both Arg-102 and Tyr-109 (or His-107 and Tyr-109) of this protein have been mutated. The fully di-AMPylated homodimer is not found in a complex with MntA. Di-AMPylated by cognate antitoxin MntA on Tyr-109 when both are expressed in E.coli; GMPylation occurs much less often. Leads to an increase of mass of 659 Da. Di-AMPylation moves the catalytic His-107 away from the catalytic center, leading to loss of nuclease activity and thus toxicity. Probably one subunit of the dimer is di-AMPylated, the complex dissociates and then reassociates to di-AMPylate the other HepT subunit. Part of a locus that includes subtype I-D CRISPR-Cas genes. Belongs to the HepT RNase toxin family. Truncated N-terminus.