Characterization of DNA polymerase. cap alpha. from Xenopus laevis, oocytes

DNA polymerase-DNA primase complex is required for eukaryotic DNA replication. They have purified this enzyme 20,000 fold from X. laevis ovaries and find its properties consistent with those reported from other eukaryotic organisms. The enzyme has an apparent native molecular weight of 480 kDa as determined by gel filtration. Activity gel analysis of the purified DNA polymerase-DNA primase complex showed the enzyme to contain a DNA polymerase catalytic subunit of 172 kDa. During purification, ion exchange chromatography removed a DNA polymerase that lacked DNA primase activity. The DNA polymerase activity had a native molecular weight of 179 kDa and a DNA polymerase catalytic subunit of 118 kDa. Both enzymes were active on the ..cap alpha.. specific template poly(dT)-oligo(rA). Using synthetic templates, they have constructed a preferred initiation sequence consisting of a 16 base pyrimidine stretch within a poly(dA) strand. Variants of this synthetic template are inactive. Further studies are in progress to define the initiation sequence utilized by the DNA polymerase-DNA primase complex on other synthetic and natural templates.