Rifampicin supersensitivity of rho strains of E. coli, and suppression by sur mutation.

Summary Escherichia coli strains with mutations rho-115, rho-ts15, rho-101 (psu-1) or rho-102 (psu-2) are more sensitive (supersensitive) to rifampicin than isogenic parent strains, as measured by growth rate in broth and colony forming efficiency on solid media with 5, 10, or 20 g of rifampicin per ml. There is no change in sensitivity of rho mutants to the antibiotics penicillin, erythromycin, chloramphenicol, or the detergent desoxycholate. The rho-101 or rho-102 mutations confer rifampicin supersensitivity at 32°C but not 42°C. Mutants of a rho-115 strain that have lost polarity suppression can be isolated by selection for rifampicin resistance. This phenotype, Sur, is not due to reversion of the original rho gene mutation but to a second mutation perhaps in the gene for rho protein or the gene for the subunit of RNA polymerase. One class of Sur mutation, occurring in rho-115 cells isolated as resistant to 20 g of rifampicin per ml, is co-transducible with the marker ilv, and the gene order is rbs-ilv-sur-38. A model suggested by this map position is that the mutations rho-115 and sur-38 define the domain of rho protein which interacts with the subunit of RNA polymerase.     

Temperature-sensitive mutant rho-115 rho-RNA binary complexes, and stabilization by substrates and analogues

Summary To determine the molecular basis for the temperature-sensitivity of pure rho RNA-dependent ATPase from Escherichia coli mutant rho-115 cells, we investigated mutant rho binding to [³H] polyC as measured by retention on nitrocellulose filters. Complexes of wild-type rho and polyC incubated at 37°C and 45°C were similarly stable. At 37°C mutant rho-polyC binary complexes were inactivated at a slightly faster rate than complexes with wild-type rho. Upon shift to 45°C the quantity of rho-115 bound to polyC declined immediately, resulting in one-fifth of the quantity of complexes observed at 37°C. Shift back to 37°C restored the level of observed complexes by two-fold. The inclusion of ATP or the analogue - methylene ATP during 45°C incubation resulted in stable mutant rho-polyC complexes. The hydrolysis product ADP was also effective in stabilizing binary complexes at 45°C but this effect was observed with an order of magnitude more ADP than ATP. Adenine, adenosine, AMP or P_i had no stabilizing effect. We conclude that the mutant rho-115 protein exhibits a structural instability as a result of binding RNA. Furthermore ATP confers a wild-type phenotype upon rho-115 protein, probably as a result of conformational change due to binding of this compound. The effect of ATP on the stability of mutant rho-polyC binary complexes supports the model of ATP modulation of rho-RNA interaction proposed by Galluppi and Richardson (1980).     

A mutant rho ATPase from Escherichia coli that is temperature-sensitive in the presence of RNA

Summary The Escherichia coli mutant rho-115 suppresses lac operon polarity conferred by the lacZ::IS1 insertion MS319. The ATPase activity of purified rho-115 protein was maximal at 40°C, in contrast to 45°C for rho ⁺. At higher temperatures (50°C, 55°C), the fractions of activities at maximal temperature were consistently lower for rho-115 compared to rho ⁺. The 30-minute time course of rho-115 ATP hydrolysis was linear at 37°C but at 45°C the linear kinetics of hydrolysis reached a plateau between 10 and 15 minutes. The 30-minute time courses for rho ⁺ were linear at both 37°C and 45°C. The rho-115 and rho ⁺ ATPase activities were equally heat-stable during preincubation at 45°C in buffer. Inclusion of ATP during preincubation protected these rho proteins from inactivation to the same extent. The presence of polyC during preincubation protected rho ^- activity but produced substantial inactivation of rho-115 ATPase. The presence of polyU during preincubation gave similar results. Concentrations of polyC between 625 ng/ml and 100 g/ml yielded the same extent of rho-115 ATPase inactivation during preincubation at 45°C. Thermal inactivation of rho-115 ATPase by polyC was halted by shifting preincubation temperature from 45°C to 35°C, indicating that polyC-induced destabilization of rho-115 was irreversible.     

Reduced superhelicity of plasmid DNA produced by the rho-15 mutation in Escherichia coli

Summary The plasmid pJSF6, a derivative of pBR327, could be maintained at 30° C in strains of Escherichia coli containing the strong rho mutation, rho-15. Plasmids extracted from rho-15 cells were always less negatively supercoiled than plasmids from rho ⁺ cells. Transduction experiments designed to separate the rho gene from possible extragenic suppressors showed that the rho allele consistently determined the degree of plasmid superhelicity. Comparison of the superhelicity of plasmids extracted from the rho-15 and from a gyrB mutant showed that at 30° C the negative supercoiling was reduced by the amounts W _rho=4.0±0.3 and W _gyr=6.0±0.3 turns; the effect of the rho-15 mutation on supercoiling was thus comparable to that of the gyrB mutation. A similar effect of the rho-15 mutation on the superhelicity of pBR329 was observed. The observation that the Rho protein has a role in determining DNA superhelicity (though not necessarily a direct role) provides a new point of view for studying the pleiotropic properties of rho mutants.We dedicate this paper to the cherished memory of Ethel S. Tessman, who died May 10, 1986. She encouraged and advised and stimulated each of us in the development of our careers     

Genetic analysis of a temperature-sensitive Salmonella typhimurium rho mutant with an altered rho-associated polycytidylate-dependent adenosine triphosphatase activity.

A conditional-lethal rho mutant of Salmonella typhimurium LT2 has been isolated. The mutation was selected as a suppressor of the polarity of an insertion sequence (IS)2-induced mutation (gal3) carried on an F' plasmid. In addition to suppression of IS2-induced polarity, the rho-111 mutation suppressed nonsense and frameshift polarity. The rho-associated polycytidylic acid-dependent adenosine triphosphatase activity in the mutant strain was elevated 15-fold above that in the parental strain, and the mutant rho protein was thermally unstable. A temperature-resistant revertant of the mutant strain did not suppress polarity and contained normal levels of polycytidylic acid-dependent adenosine triphosphatase, suggesting that the phenotype of the rho-111-bearing strain is the consequence of a single mutation. The rho-111 mutation was located on the S. typhimurium linkage map midway between the ilv and cya loci by phage P22 cotransduction studies. F' plasmid maintenance was not impaired in the mutant strain, and the mutation was recessive to the wild-type allele. The rho-111 mutation did not alter in vivo expression of either the tryptophan or histidine operons.     

Epistatic interactions of deletion mutants in the genes encoding the F1-ATPase in yeast Saccharomyces cerevisiae.

The F1-ATPase is a multimeric enzyme (alpha3 beta3 gamma delta epsilon) primarily responsible for the synthesis of ATP under aerobic conditions. The entire coding region of each of the genes was deleted separately in yeast, providing five null mutant strains. Strains with a deletion in the genes encoding alpha-, beta-, gamma- or delta-subunits were unable to grow, while the strain with a null mutation in epsilon was able to grow slowly on medium containing glycerol as the carbon source. In addition, strains with a null mutation in gamma or delta became 100% rho0/rho- and the strain with the null mutation in gamma grew much more slowly on medium containing glucose. These additional phenotypes were not observed in strains with the double mutations: Delta alpha Delta gamma, Delta beta Delta gamma, Deltaatp11 Delta gamma, Delta alpha Delta delta, Delta beta Delta delta or Deltaatp11 Delta delta. These results indicate that epsilon is not an essential component of the ATP synthase and that mutations in the genes encoding the alpha- and beta-subunits and in ATP11 are epistatic to null mutations in the genes encoding the gamma- and delta-subunits. These data suggest that the propensity to form rho0/rho- mutations in the gamma and delta null deletion mutant stains and the slow growing phenotypes of the null gamma mutant strain are due to the assembly of F1 deficient in the corresponding subunit. These results have profound implications for the physiology of normal cells.     

A novel rho promoter::Tn10 mutation suppresses and ftsQ1(Ts) missense mutation in an essential Escherichia coli cell division gene by a mechanism not involving polarity suppression.

An extragenic suppressor of the Escherichia coli cell division gene ftsQ1(Ts) was isolated. The suppressor is a Tn10 insertion into the -35 promoter consensus sequence of the rho gene, designated rho promoter::Tn10. The ftsQ1(Ts) mutation was also suppressed by the rho-4 mutant allele. The rho promoter::Tn10 strain does not exhibit rho mutant polarity suppressor phenotypes. In addition, overexpression of the ftsQ1(Ts) mutation does not reverse temperature sensitivity. Furthermore, DNA sequence analysis of the ftsQ1(Ts) allele revealed that the salt-remediable, temperature-sensitive phenotype arose from a single missense mutation. The most striking phenotype of the rho promoter::Tn10 mutant strain is an increase in the level of negative supercoiling. On the basis of these observations, we conclude that the ftsQ1(Ts) mutation may be suppressed by a change in supercoiling.     

A nuclear mutation decreasing rho- production modifies the unstable nitrous-acid sensitivity of yeast

The nuclear mmgl mutation, which reduces rho- mutability in Saccharomyces cerevisiae, renders the rho+ cells less sensitive to inactivation by nitrous acid (NA) but has little or no effect on the NA sensitivity of the rho0 cells devoid of mitochondrial (mt) DNA. Therefore the cells' NA sensitivity seems to be influenced by an interaction of the mmgl mutation and the mt genome rather than the mmgl mutation itself. The clonal variation of NA sensitivity is high in MMG+ yeast and significantly reduced in rho0 mutants and mmgl cells. The results presented suggest that frequent spontaneous heritable changes of the mt genome occur in MMG+ cells, which, (i) unlike rho- mutations, do not damage the respiratory capacity, and (ii) manifest themselves in a high clonal variation of NA sensitivity.     

Investigation of the functional interplay between the primary site and the subsite of RNase T1: Kinetic analysis of single and multiple mutants for modified substrates

We report on the functional cooperativity of the primary site and the sub-site of ribonuclease T₁ (RNase T₁; EC 3.1.27.3). The kinetic properties of the single Tyr-38-Phe and Asn-98-Ala mutants have been compared with those of the corresponding double mutant. The Tyr-38-Phe mutation has been used to probe enzyme-substrate interactions at the primary site; the Asn-98-Ala mutation monitors subsite interactions.¹ In addition to the dinucleoside phosphate substrate GpC, we measured the kinetics for GpMe, a synthetic substrate in which the leaving nucleoside cytosine has been replaced by methanol. All data were combined in a triple mutant box to analyze the interplay between Tyr-38, Asn-98, and the leaving group. The free energy barriers to k_cat, introduced by the single Tyr-38-Phe and Asn-98-Ala mutations are not additive in the corresponding double mutant. The energetic coupling between both mutations is independent of the binding of the leaving cytosine at the subsite. We conclude that the coupling of the Tyr-38-Phe and Asn-98-Ala mutations arises through distortion or reorientation of the 3′-guanylic acid moiety bound at the primary site. The experimental data indicate that the enzyme–substrate interactions beyond the scissile phosphodiester bond contribute to catalysis through the formation of new or improved contacts in going from ground state to transition state, which are functionally independent of primary site interactions. © 1994 John Wiley & Sons, Inc.     

Endocrinological findings in sterile pink-eyed mice.

Mice homozygous for rho-25h, a mutation at the pink-eye locus, are small, nervous and male sterile, with abnormal sperm morphology: females have very low fecundity. Evidence is presented that in both sexes the pars nervosa of the rho-25h/rho-25h pituitary contains degenerating nerve axons, that the hypothalamus has a reduced binding capacity for oestradiol-17 beta and that thyroid iodine binding is reduced. No changes were observed in the anterior pituitary. In rho-25h/rho-25h females, the uterus is threas-like and unresponsive to oestradiol, and the ovaries are small with many abnormal follicles. Possible modes of action of the rho locus are duscussed with reference to this and pre-existing data on the rho phenotype.     

Prolyl hydroxylase domain protein 3 targets Pax2 for destruction

Rhomboid-7 (rho-7) is a mitochondrial-specific intramembranous protease. The loss-of-function mutation rho-7 results in semi-lethality, while escapers have a reduced lifespan with several neurological disorders [1]. Here we show that general, or CNS-specific expression of rho-7 can rescue the lethality of rho-7. General, or CNS-specific over-expression of rho-7 in otherwise wild-type animals caused semi-lethality, with approximately 50% of the animals escaping this lethality, developing into adults displaying a shortened life span with larval locomotory problem. On a cellular level, over-expression resulted in severe depression of ATP levels and cytochrome c oxidase subunit II mRNA levels, a lowered number of mitochondria in neurons and aggregation of mitochondria in the brain indicating mitochondrial malfunction. Over-expression of rho-7 in developing eye discs resulted in an elevated apoptotic index. In the CNS, elevated levels of rho-7 were accompanied by both isoforms of Opa1-like, a dynamin-like GTPase, a mitochondrial component involved in regulating mitochondrial dynamics and function, including apoptosis. Most, but not all, of rho-7 over-expression phenotypes were suppressed by introducing a heterozygous mutation for Opa1-like. Our results suggest that rho-7 and Opa1-like function in a common molecular pathway affecting mitochondrial function and apoptosis in Drosophila melanogaster.     

Suppressor mutations (rin) that specifically suppress the recA+ dependence of stable DNA replication in Escherichia coli K-12

Summary The sdrA102 mutation confers upon cells the ability to replicate DNA in the absence of protein synthesis. This mutation was combined with the recA200 mutation, which renders the recA protein thermolabile, and had little effect on normal replication. However, the sdrA102 recA200 double mutant exhibited temperature-sensitive stable DNA replication: it replicated DNA continuously in the presence of chloramphenicol at 30°C, whereas at 42°C DNA replication ceased after the DNA content increased only 40–45%. Suppressor mutants (rin; recA-independent) capable of stable DNA replication at 42°C were isolated from the double mutant. The suppressor mutant retained all other recA ^– characteristics, i.e., deficient general recombination, severe UV-sensitivity, and incapability of prophage induction in lysogens. This indicates that the rin mutation specifically suppresses the recA ⁺ dependency of stable DNA replication. It is suggested that the recA ⁺ protein stabilizes a specific structure, similar to an intermediate in recombination, which may function in the initiation of stable DNA replication.     

A New Fungal Metabolite and Root Growth-stimulating Activity of Its Methyl Ester

Escherichia coli rodA mutant AOS151 grows as round cells at 30 and 42°C (H. Matsuzawa, K. Hayakawa, T. Sato, and K. Imahori, J. Bacteriol., 115, 436–442 (1973)). The mutant was found to be resistant to mecillinam at both temperatures. lip⁺ transductants were prepared by Pl phage transduction via strain AOS151, the cotransduction frequency of round morphology (Rod^?) at 42°C with the lip gene being about 90%. At 42°C all 54 Rod^? transductants tested were resistant to mecillinam. At 30°C all but two of these Rod^? (at 42°C)-type transductants were rod-shaped, and all were sensitive to mecillinam; the two strains grew as ovoid cells. The original rodA mutant AOS151 probably involves an additional mutation(s), that expresses the round cell shape at lower temperature, whereas the rodA51 mutation alone seems to result in temperature-sensitive expression of round cell morphology and mecillinam resistance. rodA mutant cells cultured at either 30 or 42°C had wild-type penicillin-binding protein 2, judging from penicillin-binding activity, electrophoretic mobility, and thermosensitivity.