Kleckner Home Page
We are interested in the fundamental processes that govern chromosome behavior. Genetic, biochemical and cytological approaches are taken to the diverse problems using both E.coli and yeast as experimental systems.
(1) Mechanism and regulation of transposition. Transposable elements move from place to place in genomes via a series of specific DNA breaking and joining events. We are analyzing the biochemical mechanism of transposition for a bacterial transposon, Tn10, which utilizes its own transposase protein in conjunction with accessory host factors. We wish to understand the precise nature and order of reaction steps, the types of DNA/protein complexes involved, the process by which the two ends of the transposon identify one another, the mechanistic role of host factors, the importance of DNA topology and the functional organization of transposase protein.
(2) Chromosome pairing and recombination during meiosis. During sexual reproduction, gametogenesis involves the halving of the cellular chromosome complement via the process of meiosis. This process requires that homologous (maternal and paternal) chromosomes recognize one another, pair along their lengths and undergo recombination. The formation of recombinants is tightly regulated. We are analyzing all of these events at the molecular level by (a) developing new assays for the processes involved, (b) identifying new genes involved in these processes, (c) carrying out biochemical analysis of relevant proteins and (d) formulating new conceptual framewords for understanding how these processes might occur.
(3) Control of replication initiation. In E.coli, as in most higher organisms, replication initiation is tightly regulated. It must occur at precisely the appropriate time in the "cell cycle" and at that time must occur once and only once. We are investigating how this regulation is achieved. We have identified a gene that is intimately involved in the regulation of replication initiation and is the first negative regulator of initiation identified in any organism. The role of this gene, and its gene product, are being investigated by biochemical and genetic approaches. Additional new approaches to the problem are also being developed.
Selected Publications:
Lu, J., Campbell, J., Boye, E. and Kleckner, N. (1994). SeqA: a negative modulator of replication initiation in E.coli. Cell 77:413-426.
Schwacha A. and Kleckner, N. (1995). Identification of double Holliday junctions as intermediates in meiotic recombination. Cell 83: 783-791.
Bolland, S. and Kleckner, N. (1996). The three chemical steps of Tn10/IS10 transposition involve repeated utilization of a single active site. Cell 84:223-233.