DNA Polymerase-Parental DNA Interaction Is Essential for Helicase-Polymerase Coupling during Bacteriophage T7 DNA...

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• DNA replication relies on coordinated action between DNA helicase and DNA polymerase at the replication fork.
• The precise molecular mechanisms of helicase-polymerase coupling remain incompletely understood.
• Recent structural data of the T7 replisome suggests a model where enzymes sandwich parental DNA.

Purpose of the Study:

• To investigate the role of specific structural features of T7 DNA polymerase in helicase-polymerase coupling and replisome progression.
• To elucidate the molecular basis of how T7 polymerase interacts with T7 helicase during DNA synthesis.

Main Methods:

• Site-directed mutagenesis was used to create T7 polymerase variants with altered beta-hairpin loops and positively charged clefts.
• In vitro assays were performed to assess strand-displacement synthesis and DNA synthesis on linear substrates.
• Synergistic binding and unwinding assays were conducted to evaluate helicase-polymerase interactions at the DNA fork.

Main Results:

• Mutations in the T7 polymerase's beta-hairpin loop and charged cleft significantly impaired strand-displacement synthesis.
• These mutations had a minimal impact on DNA synthesis using linear DNA substrates.
• The identified mutations abolished synergistic binding between helicase and polymerase, and processive fork progression.

Conclusions:

• T7 DNA polymerase plays a dominant role in the coupling with T7 helicase during DNA replication.
• Specific structural elements, including the positively charged cleft and beta-hairpin loop of T7 polymerase, are critical for efficient replisome progression.
• The findings provide new insights into the coordinated mechanism of DNA synthesis at the replication fork.