In addition to their mismatch recognition activities, bacterial and eukaryotic MutS activities have an associated ATPase activity that is required for function of the proteins in mismatch repair (1-5). Two distinct functions have been proposed for nucleotide binding and hydrolysis by MutS homologs, both of which are based on the effects of ATP on MutS-heteroduplex interaction. The presence of ATP greatly reduces the efficiency of specific complex formation between bacterial MutS or eukaryotic MutS␣ and heteroduplex DNA (5-10), and ATP challenge of preformed MutS⅐heteroduplex complexes has been shown to result in departure of the protein from the mismatch (11). Available information indicates that some of these effects are attributable to ATP binding. Thus, ATP␥S has been shown to promote departure of MutS from the mismatch in heteroduplex DNA (11), while ATP␥S or ATP (in the absence of a divalent cation) reduce the binding efficiency human MutS␣ (hMutS␣) to synthetic heteroduplexes (5, 10).Electron microscopy of complexes between bacterial MutS and large heteroduplexes prepared from natural DNAs has demonstrated that ATP-promoted release of MutS from a mismatch is associated with efficient conversion of protein⅐DNA complexes to ␣-shaped loop structures stabilized by MutS at the base (11). Loop formation requires a mismatch, loop size increases linearly with time, loop growth depends on continued ATP hydrolysis, and the mismatch usually ends up in the loop. These observations have been interpreted in terms of a mechanism in which ATP binding reduces affinity of the protein for a mispair and activates secondary DNA binding sites that are subsequently used for movement of the protein along the helix contour in a reaction dependent on nucleotide hydrolysis (11). MutS movement in this manner has been postulated to be important for the coupling of mismatch recognition to loading of the excision system at the strand break that directs repair (12, 13), a site that can be located hundreds of base pairs from this mismatch.The finding that ATP binding reduces the efficiency of specific complex formation between hMutS␣ and oligonucleotide heteroduplexes has led to proposal of a molecular switch model for action of MutS activities. Like a G-protein, hMutS␣ is postulated to exist in two states, an ADP-bound form that binds with near irreversible affinity to a mismatch and an ATPbound form that does not (10). In this proposal hMutS␣⅐ADP binds to a mispair and recruits downstream activities to this site. After assembly of the excision system, ATP binding results in dissociation of hMutS␣ from the heteroduplex so that repair may proceed (10).To further clarify the role(s) of ATP binding and hydrolysis in hMutS␣ action, we have evaluated the effects of ATP, ADP, and nonhydrolyzable ATP analogs on the lifetime of hMutS␣⅐DNA complexes and have examined the effect of DNA topology on ATP-promoted dissociation of hMutS␣ complexes with small heteroduplexes. We demonstrate that ADP is not required for mismatch recognition by hMutS␣, but...

We describe the design and implementation of a high-data-rate high-capacity digital holographic storage disk system. Various system design trade-offs that affect density and data-rate performance are described and analyzed. In the demonstration system that we describe, high-density holographic recording is achieved by use of high-resolution short-focal-length optics and correlation shift multiplexing in photopolymer disk media. Holographic channel decoding at a 1-Gbit/s data rate is performed by custom-built electronic hardware. A benchmark sustained optical data-transfer rate of 10 Gbits/s has been successfully demonstrated.

No abstract

Abstract:We discuss the design considerations of Internet Assisted Laboratories (Ilabs), their educational use for teachers and students in the classroom and for homework, and the results of several pedagogical evaluations at Stanford University of remote optics Ilabs we have used since 1998. ©2003 Optical Society of AmericaOCIS codes: (180.2520) Fluorescence microscopy; (170.2520) Fluorescence microscopy Internet-based learning extends beyond the confines of the classroom. Internet Assisted Laboratories (Ilabs) allow students and teachers access to experimental facilities from anywhere where there is an Internet connection. By controlling an actual experiment students can gain an understanding of and experience with physical phenomenon beyond that which the classroom offers. On-line experiments allow direct control of physical processes, observation of non-ideal phenomena such as noise and provide students with insight into practical limitations. By observing real physical processes under non-ideal conditions, students gain deeper physical intuition than textbooks and classroom lectures alone can offer. The Stanford Ilabs StudyAt Stanford University a pilot study was begun in 1997 with the following objectives: a) to develop a framework for integration of web-based classroom instruction and remote control of laboratory experiments; b) to implement a pilot program; c) to professionally and independently evaluate the performance and usefulness of the pilot program within the context of University learning; d) to explore new possibilities for improving classical classroom education. Since that early work, we have continued to innovate and develop new Ilabs technology and pedagogical tools. Although we have chosen optical experiments in this program, the concept of CyberLab lends itself for experimentation in almost any field, including but not limited to mechanical engineering, aeronautics, electrical engineering, physics, biology, chemistry, medicine, material science and earth sciences. Ilabs Designs and ImplementationsA functional web-based laboratory environment was created using novel Java-based technology specifically designed and implemented for Ilabs. The lab interface is designed with organization in mind that will teach good habits and etiquette. In addition to the remote control of physical experiments, the Ilabs interface also provides a lab scheduler, a reference library, course material, computer based analysis and simulation tools, testing facilities, and an electronic lab notebook. The Ilabs control software encrypts all transmissions, and allows control of equipment, even if it is located behind a firewall. New collaboration methods were developed allowing multiple users complete real-time access to data and experiments. Five optics laboratories have been implemented as well as a gas dynamics experiment, and a biology experiment using optical tweezers on nano-dimensions. A Stanford Ilabs showing optical diffraction is currently accessible at the OSA website www.optics4kids.org. Evaluation of Cyber...

No abstract