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Metal Dependency for Transcription Factor Rho Activation

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journal contribution
posted on 14.01.2003, 00:00 by Thomas P. Weber, William R. Widger, Harold Kohn
The Escherichia coli rho transcription termination factor terminates select transcripts and rho activity requires Mg2+. We investigated whether divalent metal ions other than Mg2+ catalyze rho-dependent ATP hydrolysis to ADP and Pi in vitro. The effects of 11 divalent metal ions (Be2+, Ca2+, Cd2+, Co2+, Cu2+, Hg2+, Mn2+, Ni2+, Sr2+, VO2+, Zn2+) on ATPase activity were determined in the absence and presence of MgCl2. Without MgCl2, Ca2+, Cd2+, Co2+, Cu2+, Hg2+, Mn2+, Ni2+, VO2+, and Zn2+ activated ATP hydrolysis with either hyberbolic (Ca2+, Co2+, Cu2+, Hg2+, VO2+), peak velocity (Cd2+, Mn2+, Zn2+), or sigmoidal (Ni2+) rate acceleration curves. Sr2+ was found to be a nonactivator and Be2+ an inhibitor of rho-dependent ATPase activity. The metals' effects were compared with Mg2+ and gave different rank orders when either the velocity (Vmax, Vpeak) or the efficiency (Vmax/KM, Vpeak/KM) of ATP hydrolysis was used as the determinant (V:  Mg2+ ∼ Mn2+ > Zn2+ > Co2+ > Ni2+ ∼ Cd2+ > Ca2+ > Cu2+ > Hg2+ ∼ VO2+; V/KM:  Mg2+ > Mn2+ > Ca2+ > Co2+ > Zn2+ > Cu2+ > Ni2+ > Hg2+ > Cd2+). Mg2+ proved to be the most effective divalent metal. We observed that the metal-dependent rates were affected by metal ion interactions with rho, RNA, and the buffer constituents. Significantly, replacement of the octahedral Mg2+ ion by metals that typically prefer coordination spheres less than six (Cd2+, Co2+, Ni2+, VO2+, Zn2+) led to ATPase activity, suggesting that the putative Mg·ATP2- coordination sphere in rho does not need to remain fully intact for ATP hydrolysis.