One of 2 TIR-like protein components of antiviral defense system Thoeris, composed of ThsA, TIR1 (thsB1) and TIR2 (thsB2). Phage infection activates this protein; by 70 minutes post-infection with phage SPO1, TIR1 generates a signal molecule that activates the NAD(+) hydrolase activity of ThsA (tested with B.cereus). The signal is similar to cyclic ADP-D-ribose, but how it differs is unknown. Expression of Thoeris in B.subtilis (strain BEST7003) confers resistance to phages phi29, phi3T, SPBeta, SBSphi11, SBSphi13, SBSphiJ, SPO1 and SPR but not SBSphiC. The TIR paralogs confer resistance to different phages; this subunit confers resistance to phi29, SBSphi11, SBSphi13, SBSphiJ, SPO1 and SPR but not phi3T, SBSphiC or SPBeta. There is overlap in the phage range for this system, both TIR1 and TIR2 are activated by SBSphi13, SBSphiJ, SPO1 and SPR. Activated upon phage infection. Belongs to the Thoeris B TIR-like family.