Isolation and characterization of the Escherichia coli htrB gene, whose product is essential for bacterial viability above 33 degrees C in rich media

Abstract

We have identified and studied the htrB gene of Escherichia coli. Insertional inactivation of the htrB gene leads to bacterial death at temperatures above 33°C. The mutant bacterial phenotype at nonpermissive temperatures includes an arrest of cell division followed by the formation of bulges or filaments. The htrB + gene has been cloned by complementation and shown to reside at 23.4 min on the E. coli genetic map, the relative order of the neighboring loci being mboA-htrB-pyrC. The htrB gene is transcribed in a counterclockwise fashion, relative to the E. coli genetic map, and its product has been identified as a membrane-associated protein of 35,000 Da. Growth experiments in minimal media indicate that the HtrB function becomes dispensable at low growth rates.

Function of Escherichia coli MsbA, an Essential ABC Family Transporter, in Lipid A and Phospholipid Biosynthesis

“…4 and 7), which are efficiently translocated to the outer membrane. The origin of these acylated species is not entirely clear, given that the htrB gene in MLK53 is disrupted by an insertion (17). Some of this acylation may be catalyzed by Ddg (a cold-shock induced palmitoleoyltransferase with homology to HtrB that appears to acylate the same OH group on Kdo 2 -lipid IV A normally employed by HtrB) (37).…”

“…(htrB Ϫ ) cannot grow above 32.5°C (16,17). MLK53 was labeled with 32 P i either at 30 or at 42°C for 3 h. The membrane separations and the lipid profiles of the individual fractions are shown for cells grown at 30°C (Fig.…”

“…2) (15,16). Cells harboring htrB mutations fail to grow above 32°C (17), display unusual surface bulging (17), overproduce glycerophospholipids at 42°C (17,18), and accumulate under-acylated species of lipid A (19).…”

Effect of Cold Shock on Lipid A Biosynthesis inEscherichia coli

“…As shown by Clementz et al (10,11,16), the lpxL(htrB) gene, which was initially identified as being required for growth of E. coli above 32°C (17,18), encodes the lauroyl transferase (Fig. 1).…”

“…The Palmitoleoyl Transferase Is Not Encoded by the lpxL Gene-To determine if the cold-induced activity was dependent upon the lpxL gene, we assayed the palmitoleoyl transferase activity in extracts of cold-shocked cells of strain MLK53 (17), in which the lpxL gene is inactivated by an insertion mutation.…”