A plastid-encoded DNA-directed RNA polymerase complex that resembles eubacterial multisubunit RNA polymerases with a core composed of alpha, beta, and beta-prime subunits. An additional subunit, a sigma factor, is required for promoter recognition. PEP-B is distinguished from PEP-A by its sensitivity to the antibiotic rifampicin. PEP-B is found in both etioplasts and chloroplasts, but is the predominate form in etioplasts. It forms the core of the PEP-A form; the conversion from PEP-B to PEP-A occurs during chloroplast maturation.
PEP-B