Functions Of Duplicate Recas In Myxococcus Xanthus DK1622

Myxobacteria is a type of Gram-negative bacteria,which has a good environmental adaptability and geographical characteristics of distribution,and is a dominant flora in a variety of natural environments.As a prokaryote,myxobacteria have a large genome and many repetitive genes.Therefore,myxobacteria are important experimental materials for the study of prokary otic gene duplication.RecA is a versatile protein.On the one hand,it is a recombinase,which is a central component of the process of DNA recombination repair and gene homologous recombination,mediates a series of DNA chain exchange reactions,creating a central step for homologous gene recombination.On the other hand,it is also involved in the response to DNA damage?SOS reaction?,participates in the cleavage of LexA and several related inhibitors in the SOS reaction as a protease to activate the SOS reaction.Most bacterial genomes have only one copy of recA.Although people have a deeper understanding of RecA,most of them were based on the structure,function and regulation of single-copy recA.The functional differentiation and regulatory mechanism of duplicate recAs are still poorly understood.In previous studies,it was found that there is a duplicate recA phenomenon in Bacillus and Myxobacteria.In B.megaterium,both copies of recA genes were induced by damage,and certain DNA repair ability was also shown in E.coli.Myxococcus xanthus DK1622,encoded two recA genes,recA l?MXAN₁441?and recA2?MXAN₁388?.Both RecAl and RecA2 could partially restore the ultraviolet resistance of the E.coli recA deletion mutant,but only the expression of recA2 was induced by mitomycin or nalidixic acid.However,the function of the duplicate recA genes did not involved previously,as well as in-depth exploration of molecular mechanisms and expression regulation.In this paper,Myxococcus xanthus DK1622 was used as the experimental material,and a combination of in vivo and in vitro biochemistry and molecular biology experiments and bioinformatics analysis were used to initially explain the cell function of duplicate recAs.Myxococcus xanthus DK1622 has two recA genes,recA1?MXAN₁441?and recA2?MXAN₁388?,with unknown functional differentiation.Herein,we showed that both recA genes were induced by ultraviolet?UV?irradiation but that the induction of recA l 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.We propose that the functional divergence and expression regulation of duplicate recAs might be a strategy for bacteria with a large number of repetitive sequences in their large genomes to avoid incorrect recombination.