Selective plasma treatment of the recessed regions of the elastomer stamps is shown to alter the resultant protein patterns. Fluorescence microscopy is demonstrated to be an excellent tool to discriminate between regions of microcontact printed fluorescent dye-labelled albumin in polystyrene. Atomic force microscopy and shear force microscopy are used to provide high-resolution images of the patterned protein layers. The formation and characteristics of the patterns formed by these alternative strategies is discussed.

The tumor-suppressor activity of p53 is closely related to its DNA-binding properties. It binds a number of DNA response-elements and it is likely that these share a common structural feature. Here, we present a new, general method to determine the absolute twist of exible DNA promoter sequences based on direct imaging of the topology of microcircles containing the sequences. We have used magnetically driven dynamic force microscopy ("MacMode" AFM) to observe, in solution, the conformation of 168 base-pair DNA microcircles, each containing four equally spaced copies of the waf1/cip1/p21 p53 response-element. Analysis of the images showed that the microcircles are markedly puckered with a small excess of negatively writhed molecules. The average measured values of writhe are 0.109 0.013 (for 60 positively writhed molecules) and 0.098 0.011 (for 65 negatively writhed molecules). These values lead directly to a difference in linking number for the positively and negatively writhed molecules prior to ligation, from which we derive a twist mismatch of 178 (overtwist). This is 44.5 for each 42-mer precursor containing a single waf1/cip1/p21 p53 response-element, in good agreement with the range of values deduced by indirect biochemical techniques. The two values of writhe may also be used to determine the ratio of the bending (B) to twisting (C) rigidity, yielding B/C 0.23. This is about one-third of the value for long, random-sequence DNA, suggesting that the waf1/cip1/p21 p53 response-element is extremely exible, a result that is also consistent with indirect biochemical experiments. These results support the idea, proposed by us earlier, that torsional stress may play a role in the regulation of p53 binding through modulation of twist at the binding site.

The contour length of DNA fragments, deposited and imaged on mica under buffer, was measured as a function of deposition temperature. Extended DNA molecules (on Ni-and silane-treated surfaces) contract rapidly with falling temperature, approaching the contour length of A-DNA at 2℃. The contraction is not unique to a specific sequence and does not occur in solution at 2℃ or on a surface at 25℃, indicating that it arises from a combination of low temperature and surface contact. It is probably a consequence of reduced water activity at a cold surface.

Rhodamine B-ethylenediamine-cyclodextrins (RhB-βCDen) and rhodamine B-cyclodextrins (RhB-βCD) can form inclusive complexes with many guest molecules, a reaction which can be used as a nucleic acid probe. In this paper, the most stable conformations of RhB-βCDen and RhB-βCD have been determined by fluorescence experiments and analyzed by molecular modeling simulation. The interaction between RhB-βCDen and two guest molecules, 1-borneol and cyclohexanol, has also been investigated. The results showed that RhB-βCDen has a stronger interaction with 1-borneol than with cyclohexanol. Borneol could push the three aromatic-rings of rhodamine B out of the CD cavity, while the cyclohexanol could not. The interactive sites of host andguest are also presented.

Received 26 January 1998; received in revised form 19 May 1998; accepted 20 May 1998 The results from the measurement of the fluorescence spectrum showing the binding characteristics of acridine orange (AO) and bovine serum albumin (BSA) are reported. It was found that the equilibrium constant k-4848.64 lmol1, and the number of binding sites n-0.82. Based on the mechanism of the Forster energy transference, the transfer efficiency of energy and distance between the acceptor AO and BSA were found. The interaction between AO and BSA have been verified as consistent with the static quenching procedure and the quenching mechanism is related to the energy transfer.