ABSTRACT: The interactions between bovine pancreatic ribonuclease A (RNase A) and its RNA substrate extend beyond the scissile P-O5 ′ bond. Enzymic subsites interact with the bases and phosphoryl groups of the bound substrate. Those residues interacting with the phosphoryl group comprise the P0, P1, and P2 subsites, with the scissile bond residing in the P1 subsite. Here, the function of the P0 and P2 subsites of RNase A is characterized in detail. Lys66 (P0 subsite) and Lys7 and Arg10 (P2 subsite) were replaced with alanine residues. Wild-type RNase A and the K66A, K7A/R10A, and K7A/R10A/K66A variants were evaluated as catalysts for the cleavage of poly(cytidylic acid) [poly(C)] and for their abilities to bind to single-stranded DNA, a substrate analogue. The values of kcat and Km for poly(C) cleavage were affected by altering the P0 and P2 subsites. The kcat/Km values for poly(C) cleavage by the K66A, K7A/ R10A, and K7A/R10A/K66A variants were 3-fold, 60-fold, and 300-fold lower, respectively, than that of wild-type RNase A. These values indicate that the P0 and P2 subsites contribute 0.70 and 2.46 kcal/mol, respectively, to transition-state binding. Binding experiments indicate that the P0 and P2 subsites contribute 0.92 and 1.21 kcal/mol, respectively, to ground-state binding. Thus, the P0 subsite makes a uniform contribution toward binding the ground state and the transition state, whereas the P2 subsite differentiates, binding more tightly to the transition state than to the ground state. In addition, nucleic acid binding to

Single-wall carbon nanotubes (SWNTs) are promising materials for future nanoelectronics technologies, with specific applications as nanowires,1 semiconductors for field-effect transistors2 and (bio)-chemical sensors,3 memory elements,4 etc. Chemical functional-ization of carbon nanotubes by attaching various substituents to side walls and oxidized ends has been extensively investigated, mostly with the aim to improve the solubility and processability of SWNTs.5 Except for chemical doping effects6 and suppressing the conductance via destruction of the conjugation by fluorination7 or side-wall oxidation,8 little is known about substituent-induced tuning of the electronic properties of SWNTs (although significant modulation of the SWNT conductance, including rectifying be-havior, by naturally occurring defects has been demonstrated9). On the other hand, an asymmetric functionalization (AF) of a highly polarizable SWNT with electron donor substituents at one end and

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For many technologies, smaller is synonymous with better. Shrinking the size of devices brings many advantages: more components per unit area, lower power consumption, lower cost, faster response, and higher performance. An area of