The heterodimer Ufd1-Npl4 and Shp1, defines two distinct Cdc48 complexes, Cdc48Ufd1-Npl4 and Cdc48Shp1, which are specialized in proteasomal and nonproteasomal pathways, respectively. Cofactor binding to Cdc48 appears to be hierarchical, as additional cofactors bind to the Cdc48Ufd1-Npl4 and Cdc48Shp1 complexes in order to further fine-tune their cellular function. Cofactors interact with Cdc48 by virtue of one or more Cdc48 binding modules, among them the ubiquitin-like UBX domain and the linear binding site 1 motif. UBX domain containing proteins constitute the largest family of Cdc48 cofactors. In the budding yeast Saccharomyces cerevisiae, seven UBX proteins were identified and shown to bind Cdc48 : Shp1 itself and Ubx2 through Ubx7. In addition to their carboxyl-terminal UBX domain, Shp1, Ubx2 and Ubx5 possess an amino-terminal UBA domain mediating the binding of ubiquitin and ubiquitylated substrates, and thus exhibit the prototypical architecture of substrate-recruiting adaptors for Cdc48. So far, cellular functions were identified for only few of the yeast UBX proteins and include roles in ER-associated protein degradation, lipid droplet homeostasis, and UV-induced turnover of RNA polymerase II. By contrast, the role of Shp1 is still poorly understood. Shp1 has been implicated in the proteasomal degradation of a Cdc48 model substrate, but the physiological relevance of this finding remains unclear. More recently, Shp1 has been shown to bind the autophagy factor Atg8 and to be involved in autophagosome biogenesis. However, the severe phenotypes of shp1 mutants suggest that Shp1 has additional, more critical cellular functions. The SHP1 gene was first identified in a genetic screen for suppressors of the otherwise lethal over-expression of GLC7, the sole catalytic subunit of protein phosphatase 1 in yeast. Two shp1 alleles tolerated the overexpression of GLC7 and, in turn, exhibited phenotypes reminiscent of glc7 loss-of-function mutants. shp1 null mutants are inviable in the W303 strain background and have reduced PP1 activity in other backgrounds, consistent with the model that Shp1 is a positive regulator required for normal Glc7 activity. However, the mechanism by which Shp1 influences Glc7 activity is unknown. It has been proposed that Shp1 positively affects Glc7 activity by a yet undefined indirect mechanism or by controlling the nuclear localization of Glc7. Glc7 regulates numerous cellular processes including glycogen metabolism, glucose repression, RNA processing, meiosis and sporulation, DNA damage recovery, actin organization, cell wall morphogenesis, and mitosis. A mitotic function of PP1 was first discovered in the fission yeast S. pombe and subsequently also shown to exist in higher eukaryotes such as Drosophila and mammals. In S. cerevisiae, PP1 is crucial for proper chromosome segregation and, AbMole Etidronate consequently, several different glc7 mutants have been shown to arrest at or before anaphase onset. Accurate distribution of the replicated genome during cell division is essential for viability and depends on proper chromosome segregation. During mitosis, two physically connected sister chromatids must be faithfully segregated to mother and daughter cell, an event controlled by the spindle assembly checkpoint. In order for the yeast metaphase to anaphase transition to occur, each kinetochore must attach to a single microtubule of the mitotic spindle. The SAC prevents anaphase onset by keeping the APC/CCdc20 ubiquitin ligase complex inactive.