Origin activation requires both replicative and accessory helicases during T4 infection

Area of Science:

• Molecular Biology
• Virology
• Genetics

Background:

• Bacteriophage T4 is a model for DNA replication studies.
• Viral DNA synthesis relies on recombination and multiple replication origins.
• Proteins Dda and 59 are implicated in helicase loading at origins.

Purpose of the Study:

• To investigate the role of Dda and 59 proteins in T4 DNA replication origin selection and activation.
• To understand the distinct mechanisms of T4 replication origin function.

Main Methods:

• Genome-wide, real-time assay to monitor DNA replication during T4 infection.
• Analysis of dda mutant viruses to assess origin initiation.
• Comparison of origin function with and without the 59 loading protein.

Main Results:

• dda mutant viruses showed impaired preferential initiation at origins, highlighting Dda's role in origin selection.
• At least two origins function without the 59 loading protein, indicating alternative helicase loading mechanisms.
• Both Dda-dependent and independent origins require repEB for sustained activation.

Conclusions:

• Bacteriophage T4 DNA replication involves at least two distinct classes of origins.
• Origin function requires common elements: selection/activation, replisome loading, and persistence.
• Dda accessory helicase is essential for T4 origin selection and activation.