Originally published as Genetics Published Articles Ahead of Print on September 14, 2008.

Genetics, Vol. 180, 1459-1466, November 2008, Copyright © 2008
doi:10.1534/genetics.108.093443

Genetic Analysis of MraY Inhibition by the {phi}X174 Protein E

Yi Zheng*, Douglas K. Struck*, Thomas G. Bernhardt{dagger} and Ry Young*,1

* Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843-2128 and {dagger} Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, Massachusetts 02115

1 Corresponding author: Department of Biochemistry and Biophysics, Texas A&M University, 2128 TAMU, College Station, TX 77843-2128.
E-mail: ryland{at}tamu.edu

Protein E, the lysis protein of bacteriophage {phi}X174, is a specific inhibitor of MraY, the phospho-MurNAc-pentapeptide translocase that catalyzes the synthesis of lipid I in the conserved pathway for peptidoglycan biosynthesis. The original evidence for this inhibition was the isolation of two spontaneous E-resistance mraY mutants. Here we report further genetic studies aimed at dissecting the interaction between E and MraY, using a genetic strategy that is facile, rapid, and does not depend on the availability of purified E, purified MraY, or its substrates. This system relies on the ability of mraY or its enzymatically inactive D267N allele to protect cells from lysis after induction of a chimeric {lambda}::E prophage. Using this approach, the MraY protein from Bacillus subtilis, which shares 43% sequence identity with the Escherichia coli enzyme, was found to interact weakly, if at all, with E. A potential E binding site defined by transmembrane domains 5 and 9 has been identified by isolating more mraY mutants resistant to E inhibition. Genetic analysis indicates that these E-resistant alleles fall into three classes on the basis of the affinity of the encoded proteins for MraY.