This program addresses the general question of how the various sequence elements of a plasmid genome are organized so as to ensure optimal functioning, possibly as determinants of the three dimensional configuration of plasmid DNA in vivo. It deals with several newer aspects of plasmid biology that are thought to contribute importantly to the overall organizational scheme. These include an apparent replication enhancer for pT181, a site-specific recombination function that has been identified on three different staphylococcal plasmids, site-specific relaxation complexes that have been identified for three others, and a major segment of hyphenated dyad symmetry that is present on most small plasmids from gram-positive bacteria and is required for initiation of lagging strand synthesis. It is noted that disruption of the native organization of a plasmid by various types of in vitro reconstruction often causes instability and a decrease in copy number. Attempts will be made to relate the function of some of these elements to the overall functioning of the plasmid. Two important parameters that will be explored in this connection are the ability of the plasmid to maintain a stable copy number in individual cells be efficient self-correction of random fluctuations, and the ability of the plasmid to be encapsulated by a transducing phage - which is regarded as a critical component of the inter-cell transfer of these plasmids and may involve the functioning of some of the above-mentioned sequence elements.
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