The SOS Error-Prone DNA Polymerase V Mutasome and β-Sliding Clamp Acting in Concert on Undamaged DNA and during Translesion Synthesis.

Adhirath Sikand,Myron F. Goodman,Michael M. Cox,Linda B. Bloom,Roger Woodgate,Malgorzata Jaszczur

doi:10.3390/cells10051083

Abstract

In the mid 1970s, Miroslav Radman and Evelyn Witkin proposed that Escherichia coli must encode a specialized error-prone DNA polymerase (pol) to account for the 100-fold increase in mutations accompanying induction of the SOS regulon. By the late 1980s, genetic studies showed that SOS mutagenesis required the presence of two “UV mutagenesis” genes, umuC and umuD, along with recA. Guided by the genetics, decades of biochemical studies have defined the predicted error-prone DNA polymerase as an activated complex of these three gene products, assembled as a mutasome, pol V Mut = UmuD’2C-RecA-ATP. Here, we explore the role of the β-sliding processivity clamp on the efficiency of pol V Mut-catalyzed DNA synthesis on undamaged DNA and during translesion DNA synthesis (TLS). Primer elongation efficiencies and TLS were strongly enhanced in the presence of β. The results suggest that β may have two stabilizing roles: its canonical role in tethering the pol at a primer-3’-terminus, and a possible second role in inhibiting pol V Mut’s ATPase to reduce the rate of mutasome-DNA dissociation. The identification of umuC, umuD, and recA homologs in numerous strains of pathogenic bacteria and plasmids will ensure the long and productive continuation of the genetic and biochemical journey initiated by Radman and Witkin.

Highlights

The inception of the SOS field occurred in 1953, a memorable year coincident with elucidation of the structure of DNA
After translesion DNA synthesis (TLS), pol V Mut can deactivate and is no longer able to synthesize DNA (State 3) [32,34]. This model was derived from biochemical studies with a “stand-alone” pol V Mut, purified free of RecA *, in which DNA synthesis occurred in the absence of the β-sliding processivity clamp [24,25,32]
This model was derived from biochemical studies with a “stand-alone” pol V Mut, purified free of RecA *, in which DNA synthesis occurred in the absence of the β-sliding processivity 6cloafm15p [24,25,32]

Summary

Introduction

The inception of the SOS field occurred in 1953, a memorable year coincident with elucidation of the structure of DNA. The SOS concept emerged from Jean Weigle’s surprising observation that came to be known as Weigle reactivation. Λ bacteriophage that were killed (inactivated) by exposure to UV radiation failed to lyse host Escherichia coli. Infectivity was restored in the irradiated bacteriophage when the bacteria being infected were themselves irradiated with ultraviolet light. In 1967, Evelyn Witkin proposed a far-reaching mechanism to explain W-reactivation, suggesting that a group of bacterial genes ( numbering > forty), were induced in response to chromosomal DNA damage [2]. Two regulatory genes played essential roles in the damage-inducible pathway: a repressor protein

Methods

Results

Conclusion