PrimPol, an archaic primase/polymerase operating in human cells

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• DNA replication requires primase enzymes to initiate DNA synthesis.
• Standard primases exclusively use ribonucleotides to synthesize RNA primers.
• DNA damage can stall replication forks, necessitating specialized repair or bypass mechanisms.

Purpose of the Study:

• To identify and characterize a novel primase enzyme in human cells.
• To investigate the role of this enzyme in DNA replication, particularly in the presence of DNA lesions.
• To determine the subcellular localization and functional significance of the enzyme in both nuclear and mitochondrial DNA replication.

Main Methods:

• Subcellular fractionation and immunodetection to determine PrimPol localization.
• Enzymatic assays to assess PrimPol's primase and DNA polymerase activities.
• Gene silencing and knockout studies in human and mouse cells to evaluate the functional impact of PRIMPOL ablation on DNA replication.
• Analysis of PrimPol synergy with known replicative DNA polymerases (Polγ and Polε).

Main Results:

• A novel enzyme, PrimPol, was identified with the unique ability to initiate DNA synthesis using deoxynucleotides.
• PrimPol exhibits DNA polymerase activity, enabling bypass of common oxidative DNA lesions like abasic sites and 8-oxoguanine.
• PrimPol is localized in both nuclear and mitochondrial compartments, and its activity is essential for mitochondrial DNA replication.
• PRIMPOL deficiency impairs mitochondrial DNA replication and affects nuclear DNA replication fork progression.

Conclusions:

• PrimPol represents a unique dual-function enzyme acting as both a deoxynucleotide-dependent primase and a translesion DNA polymerase.
• PrimPol plays a critical role in facilitating replication fork progression by initiating DNA synthesis downstream of lesions or bypassing them.
• The enzyme is vital for maintaining genomic integrity and efficient DNA replication in both mitochondria and the nucleus.