Probable membrane protein component of antiviral defense system Thoeris, composed of ThsA and ThsB. Expression of ThsA and ThsB in B.subtilis (strain BEST7003) confers resistance to phages SBSphiC, SBSphiJ and SPO1 (PubMed:29371424). Activation by a signal generated by ThsB leads to phage resistance (By similarity). Activated by a signal molecule generated by ThsB. When this gene is missing the Thoeris system does not confer phage resistance in B.subtilis.