A single hydrophobic cleft in the Escherichia coli processivity clamp is sufficient to support cell viability and DNA damage-induced mutagenesis in vivo

Background: The ubiquitous family of DnaN sliding processivity clamp proteins plays essential roles in DNA replication, DNA repair, and cell cycle progression, in part by managing the actions of the different proteins involved in these processes. Interactions of the homodimeric Escherichia coli beta clamp with its known partners involves multiple surfaces, including a hydrophobic cleft located near the C-terminus of each clamp protomer. Results: A mutant E. coli beta clamp protein lacking a functional hydrophobic cleft (beta(C)) complemented the temperature sensitive growth phenotype of a strain bearing the dnaN159 allele, which encodes a thermolabile mutant clamp protein (beta 159). Complementation was conferred by a beta(C)/beta 159 heterodimer, and was observed only in the absence of the dinB gene, which encodes DNA polymerase IV (Pol IV). Furthermore, the complemented strain was proficient for umuDC (Pol V) -dependent ultraviolet light (UV) -induced mutagenesis. Conclusions: Our results suggest that a single cleft in the homodimeric E. coli beta sliding clamp protein is sufficient to support both cell viability, as well as Pol III, Pol IV, and Pol V function in vivo. These findings provide further support for a model in which different Pols switch places with each other on DNA using a single cleft in the clamp.