2 GENES INVOLVED IN THE PHASE-VARIABLE PHI-C31 RESISTANCE MECHANISM OF STREPTOMYCES-COELICOLOR A3(2)

The phage growth limitation (Pgl) system of Streptomyces coelicolor co nfers resistance to phi C31 and its homoimmune phages, The positions o f the pgl genes within a 16 kb clone of S. coelicolor DNA were defined by subcloning, insertional inactivation, and deletion mapping, Nucleo tide sequencing and functional analysis identified two genes, pglY and pglZ, required for the Pgl(+) (phage-resistant) phenotype, pglY and p glZ, which mag. be translationally coupled, are predicted to encode pr oteins with M(r)s of 141,000 and 101,000, respectively, Neither protei n shows significant similarity to other known proteins, but PglY has a putative ATP/GTP binding motif. The pglY and pglZ genes are cotranscr ibed from a single promoter which appears to be constitutive and is no t induced by phage infection.