Error-prone DnaE2 Balances the Genome Mutation Rates in DK1622.

is an alpha subunit of the tripartite protein complex of DNA polymerase III that is responsible for the replication of bacterial genome. The gene is often duplicated in many bacteria, and the duplicated gene was reported dispensable for cell survivals and error-prone in DNA replication in a mystery. In this study, we found that all sequenced myxobacterial genomes possessed two genes. The duplicate genes were both highly conserved but evolved divergently, suggesting their importance in myxobacteria. Using DK1622 as a model, we confirmed that 1 () was essential for cell survival, while 2 () was dispensable and encoded an error-prone enzyme for replication. The deletion of 2 had small effects on cellular growth and social motility, but significantly decreased the development and sporulation abilities, which could be recovered by the complementation of 2. The expression of 1 was always greatly higher than that of 2 in either the growth or developmental stage. However, overexpression of 2 could not make 1 deletable, probably due to their protein structural and functional divergences. The 2 overexpression not only improved the growth, development and sporulation abilities, but also raised the genome mutation rate of . We argued that the low-expressed error-prone 2 played as a balancer for the genome mutation rates, ensuring low mutation rates for cell adaptation in new environments but avoiding damages from high mutation rates to cells.