Eukaryotic DNA replication in a chromatin context.

There has been remarkable progress in the last 20 years in defining the molecular mechanisms that regulate initiation of DNA synthesis in eukaryotic cells. Replication origins in the DNA nucleate the ordered assembly of protein factors to form a prereplication complex (preRC) that is poised for DNA synthesis. Transition of the preRC to an active initiation complex is regulated by cyclin-dependent kinases and other signaling molecules, which promote further protein assembly and activate the mini chromosome maintenance helicase.

Identification of novel single amino acid changes that result in hyperactivation of the unique GTPase, Rheb, in fission yeast.

Rheb GTPase is a key player in the control of growth, cell cycle and nutrient uptake that is conserved from yeast to humans. To further our understanding of the Rheb pathway, we sought to identify hyperactivating mutations in the Schizosaccharomyces pombe Rheb, Rhb1. Hyperactive forms of Rhb1 were found to result from single amino acid changes at valine-17, serine-21, lysine-120 or asparagine-153.

Identification of dominant negative mutants of Rheb GTPase and their use to implicate the involvement of human Rheb in the activation of p70S6K.

Rheb GTPases represent a unique family of the Ras superfamily of G-proteins. Studies on Rheb in Schizosaccharomyces pombe and Drosophila have shown that this small GTPase is essential and is involved in cell growth and cell cycle progression. The Drosophila studies also raised the possibility that Rheb is involved in the TOR/S6K signaling pathway.