secA Gene Research Articles

PrlA-mediated suppression of signal sequence mutations is modulated by the secA gene product of Escherichia coli K-12.

We studied the dependence of prlA-mediated suppression of signal sequence mutations in maltose-binding protein on cellular SecA levels in Escherichia coli. Reduction of SecA levels within the cell had strong positive and negative effects on prlA-mediated suppression, depending on the particular signal sequence mutations involved. This finding suggests that prlA and secA gene products are both components of a common export system.

Transcriptional organization within an Escherichia coli cell division gene cluster: direction of transcription of the cell separation gene envA.

A cluster of at least 14 genes, each concerned with some aspect of cell envelope growth, morphogenesis, or function, is located at 2 min on the genetic map of Escherichia coli. We located the envA cell division gene and its promoter within the cluster and determined the direction of transcription of the gene by constructing fusions between its promoter and the galK coding sequence. In addition, we identified the promoter of a possible new gene lying between envA and the secA gene. We also present evidence from gene fusion studies which shows the direction of transcription of the ftsZ(sulB) division gene. The direction of transcription is the same for all three promoters and is the same as that of all other cluster genes for which this is known. We discuss the significance of this observation, together with the fact that every gene examined in sufficient detail within the cluster appears to have its own promoter and to be able to be expressed from isolated cloned fragments. Using a novel variable-copy plasmid vector, we demonstrate that the DNA fragment containing the envA gene is not stably maintained in multiple copies. The construction of two independent, nonoverlapping deletions allows us to conclude that the envA product itself is responsible for this effect.

The use of extragenic suppressors to define genes involved in protein export in Escherichia coli.

The secA gene codes for a membrane component involved in protein export in E. coli. In order to define other genes whose products play such a role, we have characterized extragenic suppressors of a secA(Ts) mutation. These suppressors fall into at least three genetic loci. One such locus is the prlA gene, previously identified by mutations which suppress signal sequence mutants. Thus, this approach may allow the identification of new genes involved in the export process.

Regulation of a membrane component required for protein secretion in escherichia coli

We have previously described a gene, secA, which may code for a component of the secretion machinery of E. coli. Temperature-sensitive mutations in this gene lead to the cytoplasmic accumulation of precursors to a number of secreted proteins. In this paper, we describe the use of antibody to the SecA protein to characterize the cellular location and regulation of the protein. The antibody was elicited in response to a SecA-LacZ hybrid protein, produced by a strain carrying a secA-IacZ gene fusion. The secA gene product is a 92 kd polypeptide that is present in small amounts in the cell and that fractionates as a peripheral cytoplasmic membrane protein. The synthesis of the SecA protein is greatly derepressed (at least tenfold) when secretion in E. coli is blocked either in a secA ts mutant or in the presence of a MaIE-LacZ hybrid protein. We suggest that components of the secretion machinery of E. coli, such as the SecA protein, may be regulated in response to the secretion needs of the cell. When suppression of a secA am mutant is eliminated, leading to the absence of SecA protein, the synthesis of maltose-binding protein is greatly reduced. These results support a mechanism in which secretion and translation are coupled.

Identification of a new gene (secA) and gene product involved in the secretion of envelope proteins in Escherichia coli.

We have constructed lambda specialized transducing phages which carry an Escherichia coli gene (secA) involved in the secretion of certain envelope proteins. These phage have been used to show that secA is a new gene to the clockwise side of envA. The secA mutation previously described, secA5l(Ts) (D. B. Oliver and J. Beckwith, Cell 25:765-772, 1981), is recessive to the wild-type allele. We have also isolated Tn5 insertions in the gene carried on the transducing phage to further define the gene. These phage were used to infect UV-irradiated cells to allow the identification of the secA gene product as a 92-kilodalton polypeptide and to show that transcription of secA is clockwise relative to the E. coli genetic map.

Order of events in the yeast secretory pathway

The sequence of posttranslational events in the export of yeast glycoproteins has been determined with the aid of mutants that affect the secretory apparatus. Temperature-sensitive secretory mutants ( sec) of S. cerevisiae, when incubated at a nonpermissive growth temperature (37°C), accumulate intracellular precursor forms of exported glycoproteins, such as invertase, and expand or amplify one or more of three different secretory organelles. Characterization of haploid double- sec-mutant strains, with regard to the structure of the accumulated invertase and the morphology of the exaggerated organelles, allows assessment of the order in which the gene products are required, the sequence of invertase maturation steps and a pathway of secretory organelles. The transitions from one organelle to the next require energy and sec gene products. One of the mutants ( sec7) accumulates a different organelle depending on the concentration of glucose in the medium. In normal growth medium (2% glucose), a thermally irreversible structure, the Berkeley body, predominates; in low glucose (0.1%), Golgi structures accumulate thermoreversibly. The results are consistent with the following model. Secretory proteins enter the ER, where the initial steps of glycosylation occur. Nine or more sec gene products and energy are required to transfer material to a Golgi-like structure, where further glycosylation occurs. Two or more functions and energy are required to package nearly fully glycosylated proteins into vesicles that are then transported into the bud, where they fuse with the plasma membrane in a process that requires at least ten additional gene products and energy.