Interaction of host and viral regulatory mechanisms: effect of the ion cell division defect on regulation of repression by bacteriophage lambda

Saturation and specificity of the Lon protease of Escherichia coli

Lon is an ATP-dependent protease of Escherichia coli. The lon mutation has a pleiotropic phenotype: UV sensitivity, mucoidy, deficiency for lysogenization by bacteriophage lambda and P1, and lower efficiency in the degradation of abnormal proteins. All of these phenotypes are correlated with the loss of protease activity. Here we examine the effects of overproduction of one Lon substrate, SulA, and show that it protects two other substrates from degradation. To better understand this protection, we mutagenized the sulA gene and selected for mutants that have partially or totally lost their ability to saturate the Lon protease and thus can no longer protect another substrate. Some of the SulA mutants lost their ability to protect RcsA from degradation but could still protect the O thermosensitive mutant protein (Ots). All of the mutants retained their capacity to induce cell division inhibition. It was also found that deletion of the C-terminal end of SulA affected its activity but did not affect its susceptibility to Lon. We propose that Lon may have more than one specificity for peptide cleavage.

Conservation of capR (lon) DNA of Escherichia coli K-12 between distantly related species

Mutations in the capR gene of Escherichia coli K-12 are responsible for a wide variety of phenotypic changes, including defects in cell division. Since this gene plays a critical role in cell division, it might be evolutionarily conserved. Of the DNAs examined by Southern analysis, capR probe sequences were found not only in other enterics but also in Caulobacter crescentus CB13 and the distantly related archebacterium Halobacterium halobium R1.

Identification of the gene lon (capR) product as a 94-kilodalton polypeptide by cloning and deletion analysis

A mutation in the lon (capR) gene of Escherichia coli K-12 effects several phenotypic alterations in the mutant cell, such as overproduction of capsular polysaccharide and sensitivity to ultraviolet or ionizing radiation. A previously cloned 9.2-megadalton (Md) EcoRI fragment contained the capR+ gene and specified two polypeptides, 94 kilodaltons (K) and 67K. To provide evidence that the 94K polypeptide is the capR+ gene product, we constructed a capR+ plasmid pJMC40, having a 2.0-Md EcoRI-PstI fragment which codes only for the 94K polypeptide. Plasmids pJMC22 and pJMC30, having deletions of 0.7 and 0.8 Md, respectively, from one end of the 2.0-Md fragment, were also constructed. Each codes for a shortened stable polypeptide (from the 94K). Neither plasmid can confer the capR+ phenotype to capR mutants, confirming that the unaltered 94K polypeptide is the capR+ gene product. Plasmids pJMC51 and pJMC52 each have a deletion of 0.7 Md from the other end of the 2.0-Md fragment, differing only in the orientation of the remaining 1.3-Md fragment with respect to the cloning vehicle. They are nonfunctional with respect to capR+ and do not code for a common polypeptide from the 1.3-Md fragment. These data indicate that the fragments in pJMC22 and pJMC30, which both code for shortened 94K polypeptides, contain the promoter-operator region of the capR gene. The deletion plasmids were also used to map chromosomal capR mutations.

Cloning of gene lon (capR) of Escherichia coli K-12 and identification of polypeptides specified by the cloned deoxyribonucleic acid fragment

A mutation in the lon (capR) gene of Escherichia coli K-12 results in overproduction of capsular polysaccharide and increased sensitivity to ultraviolet and ionizing radiations. The lon (capR) gene deoxyribonucleic acid was cloned from a new F' factor. The new plasmids, designated pBZ201 and pBZ203, (i) contained an additional 8.2-megadalton (Md) EcoRI fragment that had the same mobility as one of the EcoRI fragments of the F', and (ii) conferred repression of capsular polysaccharide synthesis and repression of sensitivity to ultraviolet radiation in a bacterial transformation experiment with capR mutant recipient strains. A capR9 mutant plasmid, pBZ201M9, was also isolated and conferred expression of mucoidy and ultraviolet sensitivity to a capR(+) (lon(+)) strain, indicating that the capR9 allele was dominant. Plasmids pBZ201M80, pBZ201M9-INSA, and pBZ201M9-INSB were characterized by transformation as containing recessive capR mutant alleles. Heteroduplex analyses and agarose gel electrophoresis of restriction endonuclease digests of plasmid DNA preparations revealed that (i) pBZ201M9-INSA and pBZ201M9-INSB each contains a 0.5-Md insertion (probably IS1) in the cloned DNA fragment at the same site, and (ii) pBZ201 and pBZ203, both capR(+) plasmids, contain the same 8.2-Md fragment cloned in opposite orientations with respect to the cloning vehicle, pSC101. Plasmid-specified polypeptides were determined by using strain CSR603 maxicells containing each plasmid. Two new polypeptides were coded by the lon(+) (capR(+)) 8.2-Md DNA fragment: Z1, 94 kilodaltons (94K), and Z2, 67K. The maxicells containing recessive capR mutant plasmids were deficient only in synthesis of the 94K polypeptide, and the dominant (capR9) mutant plasmid specified 5 to 10 times more of the 94K polypeptide than the maxicells containing the capR(+) plasmid. Other data indicated that the capR9-specified "94K polypeptide" was not identical to the capR(+)-specified "94K polypeptide." Thus the altered mutant polypeptide was synthesized in increased quantities, suggesting a defective mode of autogenous regulation for the capR9 polypeptide and effective autogenous regulation of the capR(+) polypeptide.

Bacteriophage lambda mutants (lambdatp) that overproduce repressor

Lambda tp mutants, selected for their ability to form turbid plaques on lon hosts, overproduce repressor. The tp1 and tp2 mutations have been located within (or adjacent to) the cIII gene. The tp1 mutation reduced late gene expression, as measured by endolysin synthesis (in the absence of functional cI repressor) and progeny phage yield. The tp4 mutation was mapped in the cY-cII region, and complementation tests indicated that tp4 affects the diffusible product of the cII gene. The tp4 mutation also reduced progeny production, but did not markedly affect endolysin synthesis.

Deg phenotype of Escherichia coli lon mutants

Deg. one of the Escherichia coli systems for degrading abnormal polypeptides (e.g., nonsense fragments), is also involved in the degradation of some classes of missense proteins. Both missense proteins of beta-galactosidase and temperature-sensitive phage products appear to be degraded by the Deg system. Mutations in the Deg system are indistinguishable from mutations classically called lon or capR; all map near proC, all are mucoid, defective in protein degradation, sensitive to radiomimetic agents, and defective in P1 lysogenization. All are able to propagate temperature-sensitive phage better than lon+ parental strains. Mutations that suppress the radiation sensitivity of these strains (sul) also suppress the P1 lysogenization defect, but do not affect mucoidy or the degradation defect.