Preferential transcription of cloned maize chloroplast DNA sequences by maize chloroplast RNA polymerase

Abstract
Zea mays chloroplast DNA-dependent RNA polymerase in vitro preferentially transcribes maize chloroplast DNA sequences incorporated in cloned chimeric bacterial plasmids. Preferential transcription is dependent on the presence of a 27.5-kilodalton polypeptide, the S factor, which was purified from maize chloroplasts, and also on the template''s being in the supercoiled form.