Differential modes of DNA binding by mismatch uracil DNA glycosylase from Escherichia coli: implications for abasic lesion processing and enzyme communication in the base excision repair pathway

Mismatch uracil DNA glycosylase (Mug) from Escherichia coli is an initiating enzyme in the base-excision repair pathway. As with other DNA glycosylases, the abasic product is potentially more harmful than the initial lesion. Since Mug is known to bind its product tightly, inhibiting enzyme turnover, understanding how Mug binds DNA is of significance when considering how Mug interacts with downstream enzymes in the base-excision repair pathway. We have demonstrated differential binding modes of Mug between its substrate and abasic DNA product using both band shift and fluorescence anisotropy assays. Mug binds its product cooperatively, and a stoichiometric analysis of DNA binding, catalytic activity and salt-dependence indicates that dimer formation is of functional significance in both catalytic activity and product binding. This is the first report of cooperativity in the uracil DNA glycosylase superfamily of enzymes, and forms the basis of product inhibition in Mug. It therefore provides a new perspective on abasic site protection and the findings are discussed in the context of downstream lesion processing and enzyme communication in the base excision repair pathway

Practical active network services within content-aware gateways

© 2002 IEEE. The Internet has seen an increase in complexity due to the introduction of new types of networking devices and services, particularly at points of discontinuity known as network edges. As the networking industry continues to add revenue generating services at network edges, there is an increasing need to provide a systematic method for dynamically introducing and providing these new services in lieu of the ad-hoc approach that is in use today. To this end we support a phased approach to activating the Internet and suggest that there exists an immediate need for realizing active networks concepts at the network edges. In this context, we present our efforts towards the development of a content-aware active gateway (CAG) architecture. With the help of two practical services running on our initial prototype, built from commercial networking devices, we give a qualitative and quantitative view of the CAG potential