Nucleic Acids Research, 1984, Vol. 12, No. 19 7389-7400
© 1984
ENZYMOLOGY |
Conformationsl alterations of transcription termination protein rho induced by ATP and by RNA
Department of Chemistry, Program in Molecular, Cellular and Developmental Biology, Indiana University Bloomington, IN 47405, USA
+To whom correspondence should be addressed.
Received July 10, 1984. Revised September 5, 1984. Accepted September 5, 1984.
Transcription termination protein rho from Escherichla coli possesses an RNA-dependent ATP hydrolysis activity necessary for expression of its termination function. We have used the rate of trypsin-mediated inacti-vation of ATPase activity as a conformational probe to test for ligand binding-induced conformational changes in the rho polypeptide. When present in molar excess over rho polypeptide, trypsin inactivates rho ATPase by a first order process that correlates well with the loss of intact rho polypeptide. When rho protein binds poly(C) or poly(dC) , its susceptible bonds become more accessible to trypsin action. On the other hand, when rho binds either ATP or ADP those bonds become less accessible. These results suggest that rho protein assumes an altered conformation when an RNA cofactor is bound and that it assumes a distinctly different conformation when a nucleotide substrate or product is bound. A special change in the accessibility of trypsin-susceptible bonds is also detected when rho in its complex with poly(C) is catalyzing the hydrolysis of ATP.
*Present address: Department of Pharmacology, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06510.