THE 110-KDA POLYPEPTIDE OF SPINACH PLASTID DNA-DEPENDENT RNA-POLYMERASE - SINGLE-SUBUNIT ENZYME OR CATALYTIC CORE OF MULTIMERIC ENZYME COMPLEXES

Highly purified RNA polymerase preparations from spinach chloroplasts contain seven major polypeptides of 150, 145, 110, 102, 80, 75, and 38 kDa. I find that RNA polymerase activity can be separated under defin ed conditions into three different fractions by heparin-Sepharose chro matography. Immunological analysis has shown that the first fraction c ontains RNA polymerase activity associated with all seven major polype ptides, and other studies have shown that some of these polypeptides ( 150, 145, 80, and 38 kDa) are associated with an RNA polymerase simila r to the Escherichia coli enzyme. However, similar analyses of the rem aining fractions show activity associated only with the 110-kDa polype ptide, suggesting the existence of a second kind of chloroplast RNA po lymerase. Samples of this 110-kDa polypeptide purified by SDS/PAGE act ively synthesize RNA in a reaction dependent on a supercoiled DNA temp late and the four ribonucleoside triphosphates. Hence, this polypeptid e has all of the properties expected of a single-subunit RNA polymeras e of the T7 bacteriophage type.