Our long term goals are to understand the bacterial cell cycle and the connections among chromosome replication, organization, partitioning, and gene expression. Cell growth, propagation, and development all require the duplication and faithful segregation of chromosomal DNA. To ensure that these essential processes are proceeding normally, cells possess regulatory mechanisms that couple division or development to the fidelity of chromosomal transmission. Many diseases, including cancers, result from aberrant regulation of the cell cycle and loss of fidelity of chromosome transmission. In addition, microbial pathogenesis often depends on normal bacterial growth in the host. This proposal focuses on several aspects of the Bacillus subtilis cell cycle with three areas of particular interest related to chromosome dynamics and gene expression: 1) the regulatory response to arrest of replication forks; 2) initiation of replication and the subcellular positioning of oriC and the replisome; and 3) proteins and DNA sites involved in chromosome compaction and cohesion and their effects on gene expression. We will use a variety of approaches and methodologies to characterize: genes controlled in response to replication fork arrest; the role of DnaA, the replication initiator protein, in the transcriptional response to replication fork arrest; the subcellular positioning of the chromosomal origin of replication and its association with the membrane; the functions of two essential genes replication initiation genes; factors controlling replisome positioning in the cell; proteins involved in chromosome compaction and cohesion, and their roles in gene expression. The fundamental principles and mechanisms controlling these processes are easily studied in B. subtilis using a combination of cell biological, genetic, molecular, physiological, biochemical, and bioinformatic approaches. Because many of the proteins involved in these processes are highly conserved, insights gained from work with B. subtilis are likely to provide information regarding similar processes in a wide variety of organisms. Learning more about the essential mechanisms governing the chromosome replication and partitioning could lead to the identification of targets for the development of new antibiotics.