pEg7, a new Xenopus protein required for mitotic chromosome condensation in egg extracts

We have isolated a cDNA, Eg7, corresponding to a Xenopus maternal mRNA, whi ch is polyadenylated in mature oocytes and deadenylated in early embryos. T his maternal mRNA encodes a protein, pEg7, whose expression is strongly inc reased during oocyte maturation. The tissue and cell expression pattern of pEg7 indicates that this protein is only readily detected in cultured cells and germ cells. Immunolocalization in Xenopus cultured cells indicates tha t pEg7 concentrates onto chromosomes during mitosis. A similar localization of pEg7 is observed when sperm chromatin is allowed to form mitotic chromo somes in cytostatic factor-arrested egg extracts. Incubating these extracts with antibodies directed against two distinct parts of pEg7 provokes a str ong inhibition of the condensation and resolution of mitotic chromosomes. B iochemical experiments show that pEg7 associates with Xenopus chromosome-as sociated polypeptides C and E, two components of the 13S condensin.