Independent and Stochastic Action of DNA Polymerases in the Replisome
James E. Graham3, Kenneth J. Marians , Stephen C. Kowalczykowski4
3Present address: Oxford Nanopore Technologies, Edmund Cartwright House, 4 Robert Robinson Avenue, Oxford Science Park, Oxford OX4 4GA, United Kingdom
4Lead Contact
Article Info
Publication History
Published: June 15, 2017 Accepted: May 26, 2017
Received in revised form: March 29, 2017 Received: November 9, 2016
Highlights
• Leading- and lagging-strand polymerases function autonomously within a replisome
• Replication is kinetically discontinuous and punctuated by pauses and rate-switches
• The helicase slows in a self-regulating fail-safe mechanism when synthesis pauses
• Priming is scaled to a 5-fold reduced processivity of the lagging-strand polymerase
Summary
It has been assumed that DNA synthesis by the leading- and lagging-strand polymerases in the replisome must be coordinated to avoid the formation of significant gaps in the nascent strands. Using real-time single-molecule analysis, we establish that leading- and lagging-strand DNA polymerases function independently within a single replisome. Although average rates of DNA synthesis on leading and lagging strands are similar, individual trajectories of both DNA polymerases display stochastically switchable rates of synthesis interspersed with distinct pauses. DNA unwinding by the replicative helicase may continue during such pauses, but a self-governing mechanism, where helicase speed is reduced by ∼80%, permits recoupling of polymerase to helicase. These features imply a more dynamic, kinetically discontinuous replication process, wherein contacts within the replisome are continually broken and reformed. We conclude that the stochastic behavior of replisome components ensures complete DNA duplication without requiring coordination of leading- and lagging-strand synthesis.
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