Old and new protein in the formation of the mitotic apparatus in cleaving sea urchin eggs

It is concluded that synthesis of solubilized structural mitotic apparatus protein does not represent a heavy investment of the protein synthesis of the cell prior to the first cell division, and catalytic components necessary for mitosis may, however, be important.

Abstract

The contribution of newly synthesized cell protein to the structural proteins of the mitotic apparatus during the first cell division of sea urchin eggs was investigated. Addition of puromycin 30 minutes after fertilization reduced amino acid incorporation during the remainder of the cell cycle by more than 75%, yet the eggs undergo mitosis at 100 minutes post-fertilization. If puromycin is present from the time of fertilization, DNA replication for the ensuing mitosis occurs, but mitosis itself is prevented. Amino acid incorporation into purified, solubilized mitotic apparatus is equal to, or only slightly greater than, incorporation into bulk cell protein. About 15% of the mitotic apparatus is insoluble in salt solutions and is apparently made at much faster rates than the bulk cell protein. It is concluded that synthesis of solubilized structural mitotic apparatus protein does not represent a heavy investment of the protein synthesis of the cell prior to the first cell division. Synthesis of catalytic components necessary for mitosis may, however, be important.