Spt16 and Pob3 of Saccharomyces cerevisiae Form an Essential, Abundant Heterodimer That Is Nuclear, Chromatin-Associated, and Copurifies with DNA Polymerase α

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Abstract
Previously we showed that the yeast proteins Spt16 (Cdc68) and Pob3 are physically associated, and interact physically and genetically with the catalytic subunit of DNA polymerase α, Pol1 [Wittmeyer and Formosa (1997) Mol.Cell.Biol.17, 4178−4190]. Here we show that purified Spt16 and Pob3 form a stable, abundant, elongated heterodimer and provide evidence that this is the functional form of these proteins. Genetic interactions between mutations in SPT16 and POB3 support the importance of the Spt16−Pob3 interaction in vivo. Spt16, Pob3, and Pol1 proteins were all found to localize to the nucleus in S.cerevisiae. A portion of the total cellular Spt16−Pob3 was found to be chromatin-associated, consistent with the proposed roles in modulating chromatin function. Some of the Spt16−Pob3 complex was found to copurify with the yeast DNA polymerase α/primase complex, further supporting a connection between Spt16−Pob3 and DNA replication.