Browsing by Author "Nutt, Leta K"

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Open Access
Inhibition of the anaphase-promoting complex by the Xnf7 ubiquitin ligase.
(J Cell Biol, 2005-04-11) Casaletto, Jessica B; Nutt, Leta K; Wu, Qiju; Moore, Jonathan D; Etkin, Laurence D; Jackson, Peter K; Hunt, Tim; Kornbluth, Sally
Degradation of specific protein substrates by the anaphase-promoting complex/cyclosome (APC) is critical for mitotic exit. We have identified the protein Xenopus nuclear factor 7 (Xnf7) as a novel APC inhibitor able to regulate the timing of exit from mitosis. Immunodepletion of Xnf7 from Xenopus laevis egg extracts accelerated the degradation of APC substrates cyclin B1, cyclin B2, and securin upon release from cytostatic factor arrest, whereas excess Xnf7 inhibited APC activity. Interestingly, Xnf7 exhibited intrinsic ubiquitin ligase activity, and this activity was required for APC inhibition. Unlike other reported APC inhibitors, Xnf7 did not associate with Cdc20, but rather bound directly to core subunits of the APC. Furthermore, Xnf7 was required for spindle assembly checkpoint function in egg extracts. These data suggest that Xnf7 is an APC inhibitor able to link spindle status to the APC through direct association with APC core components.
Open Access
Mcm10 and And-1/CTF4 recruit DNA polymerase alpha to chromatin for initiation of DNA replication.
(Genes Dev, 2007-09-15) Zhu, Wenge; Ukomadu, Chinweike; Jha, Sudhakar; Senga, Takeshi; Dhar, Suman K; Wohlschlegel, James A; Nutt, Leta K; Kornbluth, Sally; Dutta, Anindya
The MCM2-7 helicase complex is loaded on DNA replication origins during the G1 phase of the cell cycle to license the origins for replication in S phase. How the initiator primase-polymerase complex, DNA polymerase alpha (pol alpha), is brought to the origins is still unclear. We show that And-1/Ctf4 (Chromosome transmission fidelity 4) interacts with Mcm10, which associates with MCM2-7, and with the p180 subunit of DNA pol alpha. And-1 is essential for DNA synthesis and the stability of p180 in mammalian cells. In Xenopus egg extracts And-1 is loaded on the chromatin after Mcm10, concurrently with DNA pol alpha, and is required for efficient DNA synthesis. Mcm10 is required for chromatin loading of And-1 and an antibody that disrupts the Mcm10-And-1 interaction interferes with the loading of And-1 and of pol alpha, inhibiting DNA synthesis. And-1/Ctf4 is therefore a new replication initiation factor that brings together the MCM2-7 helicase and the DNA pol alpha-primase complex, analogous to the linker between helicase and primase or helicase and polymerase that is seen in the bacterial replication machinery. The discovery also adds to the connection between replication initiation and sister chromatid cohesion.