Catalytic properties of DNA polymerase α activity associated with the heat‐stabilized nuclear matrix prepared from HeLa S3 cells

We have investigated whether or not ATP or other nucleoside di‐ and trisphosphates (including some nonhydrolysable ATP analogues) can stimulate the activity and/or the processivity of DNA polymerase α associated with the nuclear matrix obtained from HeLa S3 cell nuclei that had been stabilized at 37°C prior to subfractionation, as has been reported previously for DNA polymerase α bound to the nuclear matrix prepared from 22‐h regenerating rat liver. We have found that HeLa cell matrix‐associated DNA polymerase α activity could not be stimulated at all by ATP or other nucleotides, a behaviour which was shared also by DNA polymerase α activity that solubilizes from cells during the isolation of nuclei and that is thought to be a form of the enzyme not actively engaged in DNA replication. Moreover, the processivity of matrix‐bound DNA polymerase α activity was low (< 10 nucleotides). These results were obtained with the matrix prepared with either 2 M NaCl or 0·25 M (NH 4 ) 2 SO 4 and led us to consider that a 37° incubation of isolated nuclei renders resistant to high‐salt extraction a form of DNA polymerase α which is unlikely to be involved in DNA replication in vivo .