Coordinating DNA replication by means of priming loop and differential synthesis rate

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• DNA replication requires coordinated synthesis of leading and lagging strands.
• The lagging strand is synthesized discontinuously via Okazaki fragments, posing a challenge for equal synthesis rates.

Purpose of the Study:

• To elucidate the coordination mechanisms ensuring equal DNA strand synthesis rates during replication.
• To investigate the role of T7 replication proteins in coordinating leading and lagging strand synthesis.

Main Methods:

• Utilized T7 replication proteins to study DNA synthesis dynamics.
• Observed primer synthesis and polymerase activity in real-time.

Main Results:

• RNA primers are synthesized 'on the fly' during ongoing DNA synthesis.
• The leading-strand polymerase is limited by helicase speed, not primer synthesis.
• A priming loop facilitates continuous contact between primase-helicase and the replication complex.
• Lagging-strand polymerase synthesizes DNA faster than the leading-strand polymerase.

Conclusions:

• Three synergistic mechanisms coordinate DNA replication: concomitant primer synthesis, a priming loop for efficient hand-off, and faster lagging-strand polymerase activity.
• These mechanisms ensure equal net rates of leading and lagging strand DNA synthesis.
• The T7 replisome coordinates DNA synthesis without pausing during primer synthesis.