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

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Abstract
The accessibility of the s(4)U base in native tRNA(Val) from E.coli was monitored by studying the binding of various mercurials. The relative binding order HgBr(2)[unk]HgCl(2)>CH(3)HgOAc[unk]CH(3)HgCl[unk]PCMB parallels approximately the steric requirements of linear HgX(2) or RHgX compounds for S(N)2 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 Mg(2+) ions and heating to 40 degrees . Under these conditions, equilibrium dialysis measurements using (14)C-labeled PCMB showed one binding site (n = 0.93) with an association constant, K(1), of 9 x 10(4)M(-1).