Acknowledgments

We thank G.Drews for kindly providing plasmid pRCl and N.Stover and D.O'Brien for discussion.

This work was supported by the Office of Basic Energy Sciences，Biologial Energy Research Division of the U.S.Department of Energy under contract DE-ACO30-76SF00098，by U.S.Department of Agriculture grant 84 CRCR 11485，and by Public Health Service grant GM 30786 from the National Institutes of Health.The Biosearch Sam One was leased with Program Development Funds from the Director of Lawrence Berkeley Laboratory.(https://www.daowen.com)