Cell cycle aspects of the Unp ubiquitin protease.

Abstract

The product of the proto-oncogene Unp (ubiquitous nuclear protein) was shown to be localized in the nuclear fraction of COS-1 cell lysates. In situ studies using indirect immunofluorescence indicated that, when overexpressed in COS-1 cells, the Unp polypeptide localized in a perinuclear fashion. Minimal association with the microtubular structures of the cell was deduced, however neither the mechanism involved or the extent of their association have been determined. It has also been shown that the Unp protein follows a pattern of distribution, during the various phases of the cell cycle, similar to that exhibited by cyclin B1. During interphase both proteins appear perinuclear, however as the cell approaches mitosis they become 'diffuse' in their distribution. COS-1 cells expressing the Unp polypeptide displayed aberrant condensation of the chromosomes, whereas cells which did not express Unp exhibited the normal condensation pattern. Amino acid analysis of $\sp{32}$Phosphorus labeled Unp polypeptide demonstrated that it was phosphorylated on a serine residue.