Molecular Pharmacology, Vol 9, 81-92, Copyright © 1973 by the American Society for Pharmacology and Experimental Therapeutics

The Inhibition of Ribonucleic Acid Polymerase from Escherichia coli by 6-Chloro-8-aza-9-cyclopentylpurine

¹ Departments of Pharmacology and Oral Biology, The University of Michigan Medical and Dental Schools, Ann Arbor, Michigan 48104

The inhibition of RNA synthesis in vitro by the purine nucleoside analogue 6-chloro-8-aza-9-cyclopentylpurine has been characterized. This compound was found to be a noncompetitive inhibitor of the incorporation of nucleoside triphosphates into RNA by binding to DNA-dependent RNA polymerase (ribonucleoside triphosphate:RNA nucleotidyltransferase, EC 2.7.7.6) isolated from Escherichia coil. The DNA-binding and initiation functions of the enzyme were blocked, but the compound did not affect RNA chain elongation. Studies of the interactions of 6-chloro-8-aza-9-cyclopentylpurine with amino acids, N-acetylamino acid analogues, and -mercaptoethanol indicated that the drug reacts primarily with sulfhydryl groups of RNA polymerase. The inhibition could be partially reversed by dithiothreitol. The data suggest that 6-chloro-8-aza-9-cyclopentylpurine acts by inhibiting RNA polymerase function in a manner similar to the reversible sulfhydryl inhibitor p-chloromercuribenzoate.

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ACKNOWLEDGMENT The authors wish to thank Mrs. Donna Lundeen for her help in the preparation of the manuscript.