About the Authors
Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, Oklahoma, United States of America
Department of Microbiology and Immunology, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
The authors have declared that no competing interests exist.
Conceived and designed the experiments: YX JD. Performed the experiments: BK XM ZW YX JD. Analyzed the data: BK YX JD. Wrote the paper: BK YX JD.