Abstract

Former studies relying on hydrogen/deuterium exchange analysis suggest that DnaC bound to DnaB alters the conformation of the N-terminal domain (NTD) of DnaB to impair the ability of this DNA helicase to interact with primase. Supporting this idea, the work described herein based on biosensor experiments and enzyme-linked immunosorbent assays shows that the DnaB-DnaC complex binds poorly to primase in comparison with DnaB alone. Using a structural model of DnaB complexed with the C-terminal domain of primase, we found that Ile-85 is located at the interface in the NTD of DnaB that contacts primase. An alanine substitution for Ile-85 specifically interfered with this interaction and impeded DnaB function in DNA replication, but not its activity as a DNA helicase or its ability to bind to ssDNA. By comparison, substitutions of Asn for Ile-136 (I136N) and Thr for Ile-142 (I142T) in a subdomain previously named the helical hairpin in the NTD of DnaB altered the conformation of the helical hairpin and/or compromised its pairwise arrangement with the companion subdomain in each brace of protomers of the DnaB hexamer. In contrast with the I85A mutant, the latter were defective in DNA replication due to impaired binding to both ssDNA and primase. In view of these findings, we propose that DnaC controls the ability of DnaB to interact with primase by modifying the conformation of the NTD of DnaB.

Highlights

  • Former studies relying on hydrogen/deuterium exchange analysis suggest that DnaC bound to DnaB alters the conformation of the N-terminal domain (NTD) of DnaB to impair the ability of this DNA helicase to interact with primase

  • Each DnaB protomer of the DnaB ring has a RecA-like fold contained in its larger C-terminal domain (CTD)3 to which DnaC binds (19, 30 –33) and a smaller N-terminal domain (NTD) composed of two subdomains named the globular head and the helical hairpin formed by two ␣-helices (Fig. 1A) (19, 28, 34 –39)

  • The I85A, I136N, and I142T substitutions impair the ability of DnaB to interact physically with primase

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Summary

Introduction

Former studies relying on hydrogen/deuterium exchange analysis suggest that DnaC bound to DnaB alters the conformation of the N-terminal domain (NTD) of DnaB to impair the ability of this DNA helicase to interact with primase. Supporting this idea, the work described based on biosensor experiments and enzyme-linked immunosorbent assays shows that the DnaB-DnaC complex binds poorly to primase in comparison with DnaB alone. In contrast with the I85A mutant, the latter were defective in DNA replication due to impaired binding to both ssDNA and primase In view of these findings, we propose that DnaC controls the ability of DnaB to interact with primase by modifying the conformation of the NTD of DnaB. Driven by nucleotide hydrolysis during unwinding, the lagging strand DNA template is thought to pass through the DnaB toroid in the 5Ј 3 3Ј direction, whereas the other DNA strand is excluded [29, 40, 41]

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