DNA polymerase I and DNA primase complex in yeast

Area of Science:

• Molecular Biology
• Enzymology
• Yeast Genetics

Background:

• DNA replication in eukaryotes involves multiple enzymes, including DNA polymerases and primases.
• Understanding the functional relationships between these enzymes is key to elucidating replication mechanisms.
• Previous studies suggested potential interactions between yeast DNA polymerase I and primase activities.

Purpose of the Study:

• To investigate the physical and functional association between yeast DNA polymerase I and DNA primase.
• To determine if these two activities reside on separate polypeptides within a complex.
• To characterize the properties of the yeast DNA polymerase I-primase complex.

Main Methods:

• Chromatographic fractionation of yeast extracts.
• Sucrose gradient sedimentation analysis.
• Antibody inhibition assays using rabbit anti-yeast DNA polymerase I and mouse monoclonal antibodies.
• Affinity chromatography utilizing immobilized antibodies.
• Enzymatic assays for DNA polymerase and primase activities.

Main Results:

• Yeast DNA polymerase I and DNA primase activities co-fractionated and sedimented as a complex.
• Two distinct DNA polymerase I peptides (78,000 and 140,000 Da) were identified in the complex.
• Antibodies against yeast DNA polymerase I inhibited DNA polymerase activity but not primase activity, yet could precipitate the complex.
• Affinity chromatography confirmed the direct association of both activities in the complex, which could be dissociated under specific conditions.

Conclusions:

• Yeast DNA polymerase I and DNA primase exist as a functional complex in yeast extracts.
• These two enzymatic activities reside on different polypeptides.
• The complex plays a significant role in DNA replication, requiring ATP and dNTPs for poly(dT) and phage DNA replication.