secD, a new gene involved in protein export in Escherichia coli

Abstract

New mutants of Escherichia coli altered in protein export were identified in phoA-lacZ and lamB-lacZ gene fusion strains by searching for mutants that showed an altered lactose phenotype. Several mutations mapped in a new gene, secD. These mutants were, in general, cold sensitive for growth, and the mutations led to an accumulation of precursor of exported proteins. The secD gene is closely linked to tsx on the E. coli chromosome, but separable from another gene proposed to be involved in export, ssaD, which maps nearby. A plasmid carrying secD+ was identified and used to show that the mutations are recessive. The secD gene may code for a component of the cellular export machinery.

Isolation and analysis of dominant secA mutations in Escherichia coli

“…This genetic system was also capable of detecting secA autoregulatory mutants, since such mutants would fail to superrepress the secA-lacZ fusion and would result in a Lac' phenotype in our assay. As part of this screening procedure it was necessary to use Western blot- Aliquots (0.5 ml) of each culture were labeled with 10 ,uCi of Tran-35S label for 1 min followed by the addition of 0.5 ml of ice-cold 10o trichloroacetic acid. Proteins were analyzed by immunoprecipitation, polyacrylamide gel electrophoresis, and autoradiography as described previously (26) SecA in the latter model.…”

“…Genetic selections have been employed to identify a group of sec genes whose products catalyze secretion of cell envelope proteins across the plasma membrane (2). This process has been shown to require at least six proteins: the soluble SecB protein (12,13,28,29), the membrane-dissociable SecA protein (3,6,(18)(19)(20), and four integral membrane proteins, SecD (10), SecE (21,24), SecF (la), and SecY/PrlA (8,11). In addition, two different signal peptidases involved in signal peptide processing have been characterized (27,31).…”

Structural and functional aspects of the multidrug efflux pump AcrB

“…In prokaryotes, their main physiological function seems to be associated with the extrusion of noxious substrates, with notable exceptions such as the secretory accessory proteins SecDF (Gardel et al, 1987;Pogliano and Beckwith, 1994), lipid exporter MmpL7 (Camacho et al, 2001;Domenech et al, 2005) and the putative lipooligosaccharide nodulation factor exporter NolG (Baev et al, 1991). In Eukarya, however, the functionally characterized RND proteins seem to be involved in lipid homeostasis Sleat et al, 2004;Infante et al, 2008a,b) and cell morphogenesis (Taipale et al, 2002;Nakano et al, 2004).…”

Novel prlA alleles defective in supporting staphylokinase processing in Escherichia coli

“…Accumulating genetical and biochemical evidence shows the existence of export machinery which functions, in conjunction with signal sequence, in translocation of the secretory proteins across membranes. Several genes which are involved in this process have been identified in Escherichia coli (5,17,28). Some of the genes have been recognized as two types of mutants; one acts as a conditionally lethal and pleiotropically export-defective mutant (17,27,28,34), and the other acts as a suppressor for signal sequence mutations of secretory proteins without affecting general protein export (15,29,36), implying that these export factors function as they directly or indirectly interact with signal sequences of secretory protein precursors.…”