NAD(+) hydrolyzing component of antiviral defense system Thoeris, composed of ThsA and ThsB. Activated by a signal molecule generated by ThsB, by TIR1 and TIR2 from B.dafuensis or by BdTIR from B.distachyon. Upon activation binds and hydrolyzes NAD(+), leading to cell death and inhibition of phage replication. Not seen to bind DNA (PubMed:32499527, PubMed:34853457). Expression of ThsA and ThsB in B.subtilis (strain BEST7003) confers resistance to phages phi29, SBSphiC, SBSphiJ and SPO1 (PubMed:29371424, PubMed:34853457). At multiplicity of infection (MOI) of 0.05 Thoeris-encoding cultures grow normally when infected with SPO1, at MOI 5 cultures collapse prematurely by 90 minutes post-infection, thus the phage are not able to complete a replication cycle. NAD(+) levels fall and ADP-D-ribose levels rise 60 minutes post-infection. Thoeris cultures eventually recover, but retain the same susceptibility to SPO1 (PubMed:34853457). H2O + NAD(+) = ADP-D-ribose + H(+) + nicotinamide Activated by a signal molecule generated by endogenous ThsB, by TIR1 (AC A0A5B8Z670) and TIR2 (AC A0A5B8Z260) of B.dafuensis, and by BdTIR (AC I1GTC2), a plant protein involved in defense (PubMed:34853457). Activation may alter the oligomerization state of the protein (PubMed:34853457) (Probable). kcat is 33.9 min(-1) (PubMed:32499527). Homotetramer formed by dimer of dimers; homooctamers are occasionally seen. Not seen to interact with ThsB (PubMed:32499527). In the absence of the signal generated by ThsB, 63% monomer and 20% homotetramer; in the presence of the ThsB signal product 40% of the protein is dimeric (PubMed:34853457). Has an N-terminal sirtuin-like domain (SIR2, residues 1-283) and a C-terminal SLOG (STALD)-like domain (residues 284-476) (PubMed:32499527). The SIR2 domain has NAD(+) hydrolase activity (PubMed:32499527, PubMed:34853457). The C-terminus probably drives oligomerization which activates the NADase activity of the N-terminus (PubMed:34853457) (Probable). When this gene is missing the Thoeris system does not confer phage resistance in B.subtilis. Belongs to the Thoeris B TIR-like family. Truncated N-terminus.