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for kp as high as 120 L/(mol s) at 0 °C. Considering the assumptions made, this value should be taken as a lower limit.In conclusion, the anionic polymerization of e-caprolactone in tetrahydrofuran represents a living ring-chain equilibrium system. The product distribution is essentially determined by the entropy term, the lower cyclics being favored over the linear polymers at higher dilution, as expected from the Jacobson-Stockmayer theory. The very fast equilibration, as shown in this paper, should be considered in studies concerned with either or both the thermodynamics of the ring-opening polymerization and the statistics of chain conformations of the species involved.

A 55-residue protein containing the DNA binding domain of Hin recombinase, residues 139-190, with the tripeptide Gly-Gly-His (GGH) at the NH2 terminus was synthesized by stepwise solid-phase methods. GGH(Hin139-190) binds sequence specifically to DNA at four 13 base pair sites (termed hixL and secondary) and, in the presence of Ni(OAc)2 and monoperoxyphthalic acid, reacts predominantly at a single deoxyribose position on one strand of each binding site [Mack, D.P., & Dervan, P.B. (1990) J. Am. Chem. Soc. 112, 4604]. We find that, upon treatment with n-butylamine, the DNA termini at the cleavage site are 3'- and 5'-phosphate, consistent with oxidative degradation of the deoxyribose backbone. The nickel-mediated oxidation can be activated with peracid, iodosylbenzene, or hydrogen peroxide. The sequence specificity of the reaction is not dependent on oxidant, but the rates of cleavage differ, decreasing in the order peracid greater than iodosylbenzene greater than hydrogen peroxide. Optimal cleavage conditions for a 1 microM concentration of protein are 50 microM peracid, pH 8.0, and 1 equiv of Ni(OAc)2. The preferential cleavage at a single base pair position on one strand of the minor groove indicates a nondiffusible oxidizing species. A change of absolute configuration in the GGH metal binding domain from L-His to D-His [Ni(II).GG-(-D-)H(Hin139-190)] affords cleavage at similar base pair locations but opposite with regard to strand specificity.

The human immunodeficiency virus type I is strongly regulated at the transcriptional level through the interaction of an 86-amino acid protein (Tat) with a viral messenger RNA transcript. Accordingly, the binding of this protein and other cellular factors to the RNA has constituted a significant target for the development of anti-HIV drugs. In the present work, we describe the detection of the binding of two Tat-derived peptides, of 12 and 40 amino acids in length, with chemically synthesized RNA by an acoustic wave sensor. Immobilization of the nucleic acid to the sensor surface, which was incorporated in an on-line system, was effected using the biotin-neutravidin interaction. As expected, the changes in series resonance frequency and motional resistance for the two peptides indicate reversible interactions in both cases that can be further characterized by the calculation of kinetic off-rates. Of particular interest is the nature of the two frequency-based signals, which are in opposite directions for the two peptides. These results together with those obtained for the surface interactions of neutravidin and biotinylated RNA confirm that the thickness shear mode sensor, mass-response model involving the well-known Sauerbrey expression is invalid when applied to operation in liquids.