Mercury(II) binding to s4U in E.coli tRNAVal

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RESUMO

The accessibility of the s4U base in native tRNAVal from E.coli was monitored by studying the binding of various mercurials. The relative binding order HgBr2[unk]HgCl2≫CH3HgOAc[unk]CH3HgCl[unk]PCMB parallels approximately the steric requirements of linear HgX2 or RHgX compounds for SN2 displacement by sulfur, although other factors are operative. Para-chloromercuri-benzoate (PCMB) does not bind the thiolated nucleotide unless the tertiary structure of the tRNA is opened up by removal of Mg2+ ions and heating to 40°. Under these conditions, equilibrium dialysis measurements using 14C-labeled PCMB showed one binding site (n = 0.93) with an association constant, K1, of 9 × 104M−1.

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