BREX systems (bacteriophage exclusion) provide immunity against bacteriophage. Part of a type 1 BREX system which protects against dsDNA phage. This system allows phage adsorption but prevents phage DNA replication, without degradation of the phage DNA. Methylation of bacterial DNA by PglX guides self/non-self discrimination. When the brxA-brxB-brxC-pglX-pglZ-brxL genes are transformed into a susceptible E.coli strain (BW25113) they confer very high resistance to infection by bacteriophage VR7 and VpaE1, about 100-fold protection against lambda, T5 and T7 and no protection against RNA phage Qbeta, ssDNA phage M13 or dSDNA phage T4 and VR5. Glycosylated phage DNA is not susceptible to BREX. The BREX system does not confer resistance to lysogenic lambda phage, i.e. prophage that are integrated into the chromosomal DNA and then induced to form phage. Transcribed at similar levels in lag and exponential phase, rises in stationary phase. No methylation of 5'-GGTAAG-3' in chromosomal DNA, BREX no longer confers phage resistance. Belongs to the alkaline phosphatase superfamily.