Electron microscopic mapping of Thermus thermophilus RNA polymerase binding sites on plasmid pBR322

1. 1. The binding of RNA polymerase from the extreme thermophile T. thermophilus HB8 to plasmid pBR322 was measured by electron microscopy. 2. 2. DNA-protein complexes were prepared at 35 and 60°C. At both temperatures the enzyme binds strongly to sites which coincide with promoters P₁, P₂ P₃ and P₄ present in pBR322. At 60°C, an additional binding site appears, which is located between P₃ and P₄. 3. 3. There is a high degree of correlation between RNA polymerase binding sites and the location of A-T rich regions on pBR322 DNA.