Isolation and Characterization of RNA Polymerase from Vegetative and Symbiotic Forms of Rhizobium japonicum

Abstract

Summary: RNA polymerase was purified from both vegetative and symbiotic forms of Rhizobium japonicum strain 3I 1b 110 and the physical and transcriptional properties of the enzyme were compared. The subunit composition of the enzyme from both sources appeared similar when analysed by SDS-polyacrylamide gel electrophoresis. Removal of an 82 kDal protein from the purified enzyme from either source, using procedures developed for isolation of the sigma factor from Escherichia coli RNA polymerase, resulted in a decreased ability of the enzyme to utilize phage T4 DNA as a template in vitro. These results indicate that the 82 kDal protein may act as a sigma-like factor for the RNA polymerase of R. japonicum. The transcriptional specificity of the enzyme from both sources was similar using a variety of exogenous DNA templates. There were no apparent differences in the kinetic properties of the enzyme from both sources, or in the specificity of promoter utilization when phage T7 DNA was used as a template. This would indicate that a novel form of RNA polymerase may not be responsible for the transcription of nif genes in the symbiotic state.