BREX systems (bacteriophage exclusion) provide immunity against bacteriophage. Part of a type 2 BREX system (Probable). Probably a DNA methyltransferase, it methylates phage DNA in vitro in an S-adenosyl-L-methionine-dependent manner (PubMed:25592393). Previously called the phage growth limitation (Pgl) system, it confers protection against bacteriophage phiC31. The bacteria allows one cycle of phage infection, but subsequent cycles are impaired, protecting the original bacterial colony (Probable). The system undergoes high rates (10(-3) to 10(-4)) of phase reversion, i.e. loss and regain of phiC31 resistance (PubMed:8446035, PubMed:12867465). When the pglW-pglX-pglY-pglZ genes are transformed into a susceptible S.lividans (strain 1326) they confer resistance to infection by phage phiC31 and phiBT1; all 4 genes are necessary (PubMed:11972785). Probably a toxic component of a type II toxin-antitoxin (TA) system. The toxic activity is inhibited by its cognate antitoxin PglZ. May be a subtypes G and alpha restriction enzyme that recognizes and cleaves an unknown sequence. Methylates an adenine residue in the same sequence. a 2'-deoxyadenosine in DNA + S-adenosyl-L-methionine = an N(6)-methyl-2'-deoxyadenosine in DNA + H(+) + S-adenosyl-L-homocysteine Constitutively expressed, probably part of a pglW-pglX operon. Strain is no longer resistant to plaque formation by bacteriophage phiC31 (a Pgl- phenotype). Phase reversion of this Pgl system is due in part to the expansion and contraction of an 8-base long guanine tract in this protein (corresponding to residues 259-263). The tract has been observed to be 7, 8 and 9 nucleotides long in different derivatives; a 7-G tract yields a 282 residue and the 9-G tract a 336 residue missense protein. Belongs to the methyltransferase superfamily. PglX adenine methyltransferase family.