Progression of cells from interphase to mitosis involves alterations in cell structures and activities. The transition from G2 to M phase is induced by M phase promoting factor, or MPF. In M phase, many proteins are phosphorylated directly by MPF or indirectly by kinases activated by MPF. These M phase phosphoproteins (MPPs, or MPHOSPHs) permit disassembly of interphase structures and generation of M phase enzymatic activities and structures. VAM1 or MPP6 is thought to be a nucleolus specific exosome co factor, required for its role in the maturation of 5.8S rRNA.