STRUCTURAL MODULES OF THE LARGE SUBUNITS OF RNA-POLYMERASE - INTRODUCING ARCHAEBACTERIAL AND CHLOROPLAST SPLIT SITES IN THE BETA-SUBUNIT AND BETA'-SUBUNIT ESCHERICHIA-COLI RNA-POLYMERASE

The beta and beta' subunits of Escherichia coli DNA-dependent RNA poly merase are highly conserved throughout eubacterial and eukaryotic king doms. However, in some archaebacteria and chloroplasts, the correspond ing sequences are ''split'' into smaller polypeptides that are encoded by separate genes. To test if such split sites can be accommodated in to E. coli RNA polymerase, subunit fragments encoded by the segments o f E. coli rpoB and rpoC genes corresponding to archaebacterial and chl oroplast split subunits were individually overexpressed. The purified fragments, when mixed in vitro with complementing intact RNA polymeras e subunits, yielded an active enzyme capable of catalyzing the phospho diester bond formation. Thus, the large subunits of eubacteria and euk aryotes are composed of independent structural modules corresponding t o the smaller subunits of archaebacteria and chloroplasts.