Plant DNA-dependent RNA polymerases: subunit structures and enzymic properties of the class II enzymes from quiescent and proliferating tissues

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Abstract
Class II DNA-dependent RNA polymerases were purified from soybean [Glycine max] tissues of different physiological states: from seed embryo tissue, representative of a quiescent, low metabolic state and from auxin-treated hypocotyl tissue, representative of a highly proliferative and metabolically active state. Dodecyl sulfate, polyacrylamide gel electrophoresis indicates that RNA polymerase II from embryonic tissue consists largely (90-95%) of the form IIA enzyme, the largest subunit having a MW of 215,000. RNA polymerase II from hypocotyl tissue is exclusively a form IIB enzyme, the largest subunit having a MW of 180,000. Polypeptides common to RNA polymerases IIA and IIB have the following MW: 138,000, 42,000, 27,000, 22,000, 19,000, 17,600, 17,000, 16,200, 16,100 and 14,000. Peptide mapping in the presence of dodecyl sulfate suggests that the 215,000 and 180,000 subunits possess similar peptide fragments. Plant embryo tissues do not contain protease activity capable of cleaving the 215,000 subunit to the 180,000 subunit, but proliferating plant tissues do contain such an activity. Mixing experiments indicate that appreciable amounts of RNA polymerase IIB are not being artifactually produced during protein purification.