[Modification of RNA polymerase from Escherichia coli by fluoresceinbimercuriacetate]

RNA polymerase was modified by fluoresceinbimercuriacetate (FMA) at SH-groups. One molecule of the enzyme (M. W. 500,000) was shown to bind two molecules of FMA. The first molecule reacts with the most reactive SH-groups causing 50%-inhibition of RNA synthesis. The binding of the second one results in 100%-inactivation of the enzyme. Considerable changes in spectral properties of the dye are observed when it interacts with RNA polymerase.