Electron mimcroscopic imaging of theE. ColiRNA polymerase during transcription

Abstract

RNA polymerase is an enzyme found in all cellular organisms, and functions to direct the synthesis of RNA using double stranded DNA as a template. The best characterized form of the enzyme is from the enteric gram-negative bacterium, E. coli. Like other RNA polymerases, theE. colienzyme contains several tightly associated subunits; these include two large subunits, β' (155 kDA) and β (150 kDa) , two copies of a smaller subunit, α (35 kDA), and up to two copies of another small subunit, ω (11 kDA). Another more loosely associated subunit, the a factor (70 kDa), is bound to the polymerase only at the initiation step of RNA biosynthesis, and is involved in promoter recognition. The goal of this study was to gain an understanding of the structural organization of the transcribing RNA polymerase, using high resolution electron microscopic imaging and digital image processing, as well as chemical cross-linking methods.