Temperature Sensitivity and Cell Division Defects in an Escherichia coli yghB/yqjA Double Mutant, Encoding Related and Conserved Inner Membrane Proteins

Department of Biological Sciences, Socolofsky Microscopy Center, Louisiana State University, Baton Rouge, LA 70803

^* To whom correspondence should be addressed. Email: wdoerr{at}lsu.edu.

	Abstract

Ludox density gradients were used to enrich for Escherichia coli mutants with conditional growth defects and alterations in membrane composition. A temperature sensitive mutant named Lud135 was isolated with mutations in two related, nonessential genes: yghB and yqjA. YghB harbors a single missense mutation (G203D) and yqjA contains a nonsense mutation (W92TGA) in Lud135. Both mutations are required for the temperature sensitive phenotype: targeted deletion of both genes in a wild type background results in a strain with a similar phenotype and expression of either gene from a plasmid restores growth at elevated temperatures. The mutant has altered membrane phospholipid levels, with elevated levels of acidic phospholipids, when grown under permissive conditions. Growth of Lud135 under nonpermissive conditions is restored by the presence of millimolar concentrations of divalent cations Ca²⁺, Ba²⁺, Sr²⁺ or Mg²⁺ or 300-500 mM NaCl but not 400 mM sucrose. Microscopic analysis of Lud135 demonstrates a dramatic defect at a late stage of cell division when cells are grown under permissive conditions. YghB and yqjA belong to the conserved and widely distributed dedA gene family for which no function has been reported. The two ORFs encode predicted polytopic inner membrane proteins with 61% amino acid identity. It is likely that YghB and YqjA play redundant but critical roles in membrane biology that are essential for completion of cell division in E. coli.