Intact DNA polymerase alpha/primase from mouse cells. Purification and structure

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Mammalian DNA polymerase alpha/primase is essential for DNA replication.
• Previous studies reported proteolysis and subunit loss in purified mammalian enzyme complexes.
• The intact structure and precise molecular mass of mammalian DNA polymerase alpha/primase remained unclear.

Purpose of the Study:

• To describe a purification procedure for DNA polymerase alpha/primase from cultured mouse lymphoblasts.
• To characterize the subunit composition and molecular mass of the purified enzyme complex.
• To compare the structure of the mouse enzyme with homologous enzymes from other species.

Main Methods:

• Conventional protein purification techniques applied to cultured mouse lymphoblasts.
• Analysis of subunit composition using denaturing gel electrophoresis.
• Determination of molecular mass and structural properties using sedimentation coefficient and Stokes radius.

Main Results:

• Successfully purified approximately 0.5 mg of enzyme free of detectable contaminants from 40 g of cells.
• The purified mouse DNA polymerase alpha/primase contains four intact subunits (180, 70, 56, and 47 kDa).
• The native enzyme complex has an estimated molecular mass of 353 kDa (gel) or 344 kDa (sequence data), with a calculated frictional ratio of 1.80, indicating an extended structure.

Conclusions:

• A robust purification method for intact DNA polymerase alpha/primase from mouse cells was established.
• The native mammalian enzyme complex consists of four distinct subunits, maintaining structural integrity.
• The findings clarify the molecular structure of mammalian DNA polymerase alpha/primase, resolving previous discrepancies.