BREX systems (bacteriophage exclusion) provide immunity against bacteriophage. A core protein of a type 1 BREX system. This system allows phage adsorption but prevents phage DNA replication, without degradation of the phage DNA. Methylation of bacterial DNA by PglX probably guides self/non-self discrimination. When the brxA-brxB-brxC-pglX and pglZ-brxL operons are transformed into a susceptible B.subtilis strain (BEST7003) they confer resistance to bacteriophages SPbeta, SP16, Zeta, phi3T and SP02 and partial protection to phages SP01 and SP82G (these include lytic and temperate phage). They do not protect against phages phi105, rho10 or rho14. Additionally confers a very slight reduction in efficiency of plasmid transformation. Part of the pglZ-brxL operon. Belongs to the alkaline phosphatase superfamily.