Studies on changes in DNA polymerase activity during the cell cycle in synchronized KB cells

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• DNA polymerases are essential enzymes for DNA replication and repair.
• Understanding the distinct roles and regulation of different DNA polymerases is crucial for comprehending cell cycle progression and genomic stability.

Purpose of the Study:

• To identify and characterize DNA polymerases in KB cells.
• To investigate the cell cycle-dependent variations in the activity of these enzymes.
• To elucidate the potential roles of nuclear and cytoplasmic DNA polymerases in DNA duplication.

Main Methods:

• Studied synchronous KB cell populations to analyze enzyme activity throughout the cell cycle.
• Fractionated cells to isolate nuclear and cytoplasmic components.
• Assayed DNA polymerase activities using native and denatured DNA substrates.
• Determined enzyme properties including Mg++, K+ requirements, and pH optima.

Main Results:

• Identified two distinct DNA polymerases: a nuclear 3.4 S minipolymerase and a cytoplasmic 8.3 S maxipolymerase.
• Nuclear minipolymerase prefers native DNA, while cytoplasmic maxipolymerase prefers denatured DNA.
• Nuclear minipolymerase activity peaks in the S phase and fluctuates across the cell cycle, whereas cytoplasmic maxipolymerase activity remains stable.
• Observed different Mg++, K+ requirements and pH optima for the two enzymes.

Conclusions:

• The nuclear minipolymerase plays a predominant role in DNA duplication.
• The cytoplasmic maxipolymerase may function as a precursor or storage form for the nuclear minipolymerase.
• Cell cycle-dependent regulation of nuclear DNA polymerase activity is significant for DNA synthesis.