New suppressors of signal-sequence mutations, prlG, are linked tightly to the secE gene of Escherichia coli.

Abstract

Analysis of more than 100 extragenic suppressors of the lamB14D signal-sequence mutation {changes Val in the hydrophobic core region at position 14 to Asp) has revealed alterations that appear to lie at prlA (secYJ and secA {prlD), two loci known to be mutable to suppressor alleles, and a new suppressor termed priG. One allele of the new suppressor class, priG1, has been characterized in some detail. This suppressor counteracts, to some degree, the export defect conferred by a variety of signal-sequence mutations in two different genes, lamB and malE. Genetic analysis shows that the dominant suppressor mutations are linked tightly to, and probably allelic with, the gene secE. This result, coupled with data obtained with conditional-lethal alleles of secE (see accompanying paper by Schatz et al.), argues strongly that SecE is an important component of the cellular protein export machinery in Escherichia coli.

Effect of signal sequence alterations on export of levansucrase in Bacillus subtilis

“…The expression of levansucrase in E. coli has limited the construction of some signal sequence Isolation of suppressor mutations for some of the E. coli signal sequence mutants has resulted in the identification of the various genes involved in the secretion machinery in E. coli. (1,5,25). We are currently isolating suppressor mutations of defective levansucrase signal peptides in B. subtilis.…”

“…Signal sequence mutants of E. coli have aided both in understanding the role of signal sequences in the secretion process and in identifying E. coli genes involved in protein secretion (1,3,5,25). The mechanism of protein secretion in Bacillus subtilis has not been extensively studied, and few signal sequence mutants of B. subtilis have been reported (18,21).…”

A new suppressor of a lamB signal sequence mutation, prlZ1, maps to 69 minutes on the Escherichia coli chromosome

“…Since lamB14D causes a severe export defect, it is possible that the failure ofpriZI to suppress this mutation is a matter of degree rather than allele specificity, i.e., priZI is simply too weak. This degree of suppression is reminiscent of priGI, whose effect could be shown in a pulse-chase assay of the leaky lamB17D signal sequence mutation (24). Accordingly, we examined the ability of prlZl to increase the rate of signal sequence processing of LamB17D and found that the suppressor had no effect (data not shown).…”

“…Strain construction by P1 transduction was performed as previously described (21). PD1 was constructed by using STA19R as the recipient and TST6 (malF::TnlO [24]) as the donor and selecting for tetracycline resistance. PD50C was one of the Dex+ and Xs revertants of STA19R.…”

“…The lamBA60 mutation (10), resulting in the deletion of residues 10 through 21 of the LamB signal sequence, gave rise to suppressor alleles in the pril/secY gene (9). The lamB14D mutation, which results in a substitution of Asp for Val at residue 14 (10,23), gave rise to suppressor alleles in the prl/secY, prlDlsecA, and prlGlsecE genes (24). It has recently been suggested that most, if not all, prlA suppressor alleles act by decreasing the selectivity of the translocator for signal sequence-containing polypeptides (19).…”