Functional Division Between the RecA1 and RecA2 Proteins in Myxococcus xanthus

Duo-Hong Sheng,Jin-Yi Zhao,Xin-Jing Yue,Yi-Xue Wang,Yue-Zhong Li,Miao Qiu

doi:10.3389/fmicb.2020.00140

Abstract

Myxococcus xanthus DK1622 has two RecA genes, recA1 (MXAN_1441) and recA2 (MXAN_1388), with unknown functional differentiation. Herein, we showed that both recA genes were induced by ultraviolet (UV) irradiation but that the induction of recA1 was more delayed than that of recA2. Deletion of recA1 did not affect the growth but significantly decreased the UV-radiation survival, homologous recombination (HR) ability, and induction of LexA-dependent SOS genes. In contrast, the deletion of recA2 markedly prolonged the lag phase of bacterial growth and increased the sensitivity to DNA damage caused by hydrogen peroxide but did not change the UV-radiation resistance or SOS gene inducibility. Protein activity analysis demonstrated that RecA1, but not RecA2, catalyzed DNA strand exchange (DSE) and LexA autocleavage in vitro. Transcriptomic analysis indicated that RecA2 has evolved mainly to regulate gene expression for cellular transportation and antioxidation. This is the first report of functional divergence of duplicated bacterial recA genes. The results highlight the evolutionary strategy of M. xanthus cells for DNA HR and genome sophistication.

Highlights

RecA, an ATP-dependent recombinase, is the core enzyme for DNA homologous recombination (HR), as well as being a promotion agent for LexA autolysis in bacteria (Lusetti and Cox, 2002)
The recA gene is duplicated in some bacterial cells, its functions have not been investigated
The two RecA proteins are both involved in UV resistance, probably for different lesions caused by UV irradiation (Sinha and Häder, 2002); RecA2 is involved in the early repair processes, and RecA1 is involved in serious DNA-damage repair, i.e., post-replication repair

Summary

Introduction

RecA, an ATP-dependent recombinase, is the core enzyme for DNA homologous recombination (HR), as well as being a promotion agent for LexA autolysis in bacteria (Lusetti and Cox, 2002). After binding to ssDNA, the RecA/ssDNA filament complex may serve as a signal of DNA damage, resulting in the self-cleavage of LexA, which activates the SOS response, increasing the expression of LexA-repressed genes. In the best characterized Escherichia coli SOS response, LexA autolysis derepresses the expression of more than 40 genes involved in DNA repair, mutagenesis, and many other cellular processes (Cox, 2003, 2007; Maslowska et al, 2019). Because of its pros and cons in genomic stability and variability, the functions of RecA are strictly regulated; for example, the function of RecA in E. coli is regulated at the gene transcription and protein activity levels. In the gene transcription induced by the Functional Differentiation of RecAs

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