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At least 181 records · Page 10Linked to original sources
PubMed2000

A novel reverse-genetic approach (SIMF) identifies Mutator insertions in new Myb genes.

We have developed a new strategy designated SIMF (Systematic Insertional Mutagenesis of Families), to identify DNA insertions in many members of a gene family simultaneously. This method requires only a short amino acid sequence conserved in all members of the family to make a degenerate oligonucleotide, and a sequence from the end of the DNA insertion. The SIMF strategy was successfully applied to the large maize R2R3 Myb family of regulatory genes, and Mutator insertions in several novel Myb genes were identified. Application of this technique to identify insertions in other large gene families could significantly decrease the effort involved in screening at the same time for insertions in all members of groups of genes that share a limited sequence identity.

Amino Acid Sequence↗
PubMed1998

Blue light- and genetically-reversed gravitropic response in protonemata of the moss Ceratodon purpureus.

In darkness, protonemal filaments of Ceratodon purpureus (Brid.) grow negatively gravitropically (upwards). Red light induces a positive phototropic response mediated by the photoreceptor phytochrome. A red light treatment also has an inhibitory effect on the gravitropic response, an effect also mediated by phytochrome. In this study the effects of blue light on phototropism and on gravitropism were analysed. Unilateral blue light resulted in only a weak phototropic response, but markedly randomised growth direction. Blue light given together with a gravitropic stimulus reversed the gravitropism, changing it from negative to positive (filaments grow downward). The effect of blue light was also analysed with the mutant ptr116, which is defective in the biosynthesis of the phytochrome chromophore, and in a newly isolated mutant wwr2, which is positively gravitropic in darkness. Blue light induced the same reversal of gravitropism in ptrll6 as in the wild type, indicating that phytochrome is not involved in this process. In wwr2 the direction of gravitropism was unaltered by the blue light treatment. Light also affects chlorophyll content and the size of plastids, potential statoliths for gravitropism. Red light induced an increase in plastid size and chlorophyll content in the wild type but not in ptr116. Blue light induced a similar change in wild type plastids. It seems as though light-induced alterations of gravitropism are not simply mediated by alterations in plastid properties, and that red light and blue light evoke fundamentally different responses.

Bryopsida↗
PubMed2002

Reverse genetic approaches in plants and yeast suggest a role for novel, evolutionarily conserved, selenoprotein-related genes in oxidative stress defense.

Oxidation of methionine residues during periods of oxidative stress can lead to loss of protein function. Organisms have developed defense strategies to minimize such damage. The PilB protein, which is involved in pilus formation in the pathogen Neisseria gonorrhoeae, is composed of three functional protein domains (I-III) with putative roles in oxidative stress defense. These domains are evolutionarily conserved and homologs have been discovered in diverse prokaryotes and eukaryotes. Domain III shows similarities to selenoproteins which contain selenium instead of sulfur in a conserved cysteine residue. The substitution of selenium for sulfur alters the redox properties of such proteins. Knock-out mutants were used to elucidate the function of these novel selenoprotein-like domains in yeast and in Arabidopsis thaliana. We show that organisms with non-functional genes for selenoprotein-like polypeptides accumulate higher levels of oxidized methionine residues on exposure to oxidative stress. The behavior of the mutants suggests that these novel selenoprotein-like gene products are part of a ubiquitous detoxification system that interacts with other redox-related proteins such as the thioredoxin-related protein and methionine sulfoxide reductase which are encoded by domains I and II of PilB. These proteins may be encoded by one gene as in the case of several prokaryotes, or by separate genes as in the eukaryotes examined here.

Amino Acid Sequence↗
PubMed2004

Reverse genetic analysis of the glutathione metabolic pathway suggests a novel role of PHGPX and URE2 genes in aluminum resistance in Saccharomyces cerevisiae.

We have taken a systematic genetic approach to study the potential role of glutathione metabolism in aluminum (Al) toxicity and resistance, using disruption mutants available in Saccharomyces cerevisiae. Yeast disruption mutants defective in phospholipid hydroperoxide glutathione peroxidases (PHGPX; phgpx1 Delta, phgpx2 Delta, and phgpx3Delta), were tested for their sensitivity to Al. The triple mutant, phgpx1 Delta/2Delta/3Delta, was more sensitive to Al (55% reduction in growth at 300 microM Al) than any single phgpx mutant, indicating that the PHGPX genes may collectively contribute to Al resistance. The hypersensitivity of phgpx3Delta to Al was overcome by complementation with PHGPX3, and all PHGPX genes showed increased expression in response to Al in the wild-type strain (YPH250), with maximum induction of approximately 2.5-fold for PHGPX3. Both phgpx3Delta and phgpx1Delta/2Delta/3Delta mutants were sensitive to oxidative stress (exposure to H(2)O(2) or diamide). Lipid peroxidation was also increased in the phgpx1Delta/2Delta/3Delta mutant compared to the parental strain. Disruption mutants defective in genes for glutathione S-transferases (GSTs) (gtt1Delta and gtt2Delta), glutathione biosynthesis (gsh1Delta and gsh2Delta), glutathione reductase (glr1Delta) and a glutathione transporter (opt1Delta) did not show hypersensitivity to Al relative to the parental strain BY4741. Interestingly, a strain deleted for URE2, a gene which encodes a prion precursor with homology to GSTs, also showed hypersensitivity to Al. The hypersensitivity of the ure2Delta mutant could be overcome by complementation with URE2. Expression of URE2 in the parental strain increased approximately 2-fold in response to exposure to 100 microM Al. Intracellular oxidation levels in the ure2Delta mutant showed a 2-fold (non-stressed) and 3-fold (when exposed-to 2 mM H(2)O(2)) increase compared to BY4741; however, the ure2Delta mutant showed no change in lipid peroxidation compared to the control. The phgpx1Delta/2Delta/3Delta and ure2Delta mutants both showed increased accumulation of Al. These findings suggest the involvement of PHGPX genes and a novel role of URE2 in Al toxicity/resistance in S. cerevisiae.

Aluminum↗
PubMed2004

A reverse genetic approach for generating gene replacement mutants in Ustilago maydis.

We describe a versatile strategy for generating gene replacement mutants in the phytopathogenic fungus Ustilago maydis. The system includes the choice of 32 different insertion cassettes for genetic engineering purposes, such as gene disruption and more sophisticated insertions of reporter genes, heterologous promoters or combinations of the two. PCR-amplified flanking sequences needed for homologous recombination are ligated to the respective insertion cassettes via SfiI sites. As proof of principle we generated two replacement mutants in which the endogenous promoter of the pheromone gene mfa1 drives expression of the Green Fluorescent Protein gene (gfp). Simultaneously, expression of the mfa1 ORF is controlled either by the carbon source-regulated crg1 promoter or the nitrogen source-regulated nar1 promoter. In both cases gfp expression was pheromone-inducible and pheromone expression was only detected when the heterologous promoters were active.

Base Sequence↗
PubMed1994

Reverse genetics of Drosophila brain structure and function.

A set of molecular genetic technologies are described, which will have far reaching consequences for the study of brain structure, function and development in Drosophila melanogaster. Site selected mutagenesis (a PCR-based screen for P-element insertion events) allows insertion mutants to be isolated for any cloned gene, and is being used in this laboratory to ask questions about the rolls of particular cellular components in learning and memory. Transposants have been isolated in genes encoding a regulatory (RI) and a catalytic (DCO) subunit of cAMP-dependent protein kinase, and in a gene encoding a Gi-like alpha subunit. The alternative use of I factors is described. The PKA RI homozygous mutants display a significant decrement in initial learning ability. Enhancer-trap strategies, for which the GAL-4 P-element system is particularly convenient, allow the identification of genes expressed in the developing fly brain. Strategies for the efficient detection of such events are described.

Animals↗
PubMed1991

A wide-host-range suicide vector for improving reverse genetics in gram-negative bacteria: inactivation of the blaA gene of Yersinia enterocolitica.

A new suicide vector (pKNG101) that facilitates the positive selection of double recombination events in Gram-bacteria has been developed. It contains a conditional origin of replication (oriR6K), the strAB genes encoding the streptomycin phosphotransferase (SmR), an origin of transfer (mobRK2), the sacB gene mediating sucrose sensitivity, and multiple cloning sites. It was used to mutate the blaA gene of Yersinia enterocolitica, by marker-exchange mutagenesis. To do this, we have first cloned into the suicide vector pKNG101, a 2.5-kb fragment of Y. enterocolitica chromosomal DNA encoding the 20-kDa beta-lactamase A. Gene blaA was then mutated in vitro by insertion of luxAB, which resulted in pKNG105. The disrupted blaA gene was then reintroduced into Y. enterocolitica chromosome by homologous recombinations in two steps. First, E. coli SM10 lambda pir (pKNG105) was mated with strains of Y. enterocolitica. This led to the integration of pKNG105 into the chromosome, by a single homologous recombination event. The transconjugants, selected for SmR, were sensitive to sucrose due to the synthesis of levans (toxic compounds), catalysed by levansucrase, the product of sacB. For the second step, a single colony from the first step was grown in rich medium deprived of antibiotic, allowing the occurrence of a second crossing-over that replaced the wild-type allele blaA with the mutant one, and then excised the plasmid-borne sacB from the chromosome. Such blaA mutants were selected on their ability to grow on TSA medium containing 5% sucrose.(ABSTRACT TRUNCATED AT 250 WORDS)

DNA Replication↗
PubMed2005

Human parainfluenza virus type I (HPIV1) vaccine candidates designed by reverse genetics are attenuated and efficacious in African green monkeys.

A set of recombinant, live attenuated human parainfluenza virus type 1 (rHPIV1) vaccine candidates was evaluated for attenuation, immunogenicity, and protective efficacy in African green monkeys (AGMs). Temperature sensitive (ts) and non-ts attenuating (att) mutations in the P/C and L genes were introduced individually or in various combinations into rHPIV1, including the C(R84G) and HN(T553A) mutations identified in the present work and the C(F170S), L(Y942A), and L(L992C) mutations identified previously. The rHPIV1 vaccine candidates exhibited a spectrum of attenuation in AGMs. One genetically and phenotypically stable vaccine candidate, rC(R84G/F170S)L(Y942A/L992C), was attenuated and efficacious in AGMs and is a promising live attenuated intranasal HPIV1 vaccine candidate suitable for clinical evaluation.

Animals↗
PubMed2005

Influenza A virus-induced apoptosis is a multifactorial process: exploiting reverse genetics to elucidate the role of influenza A virus proteins in virus-induced apoptosis.

Three influenza viruses, A/Puerto Rico/8/34-A/England/939/69 clone 7a (H3N2), A/Fiji/15899/83 (H1N1), and A/Victoria/3/75 (H3N2), induce different levels of apoptosis in vitro at equal moi; Clone 7a > A/Victoria > A/Fiji. Previous studies have shown that several viral proteins from clone 7a and A/Fiji, including PB2, NA, NS1, M1, and M2, induce apoptosis when expressed individually fused to the herpes simplex virus tegument protein, VP22. However, this did not reflect viral protein-protein-RNA interactions known to occur within infected cells. To explore the role of viral proteins in apoptosis under infection conditions, recombinant viruses with single or triple gene exchanges were generated using A/Victoria or clone 7a as the background virus. Inserting the A/Fiji NS or PB2 gene into A/Victoria or clone 7a significantly reduced the level of apoptosis compared to the parent virus while clone 7a PA or NP genes increased apoptosis. Inserting A/Fiji NA or HA or clone 7a NS, M, NA, or HA genes individually into A/Victoria had no significant effect on apoptosis. Surprisingly, inserting the M, NA, and HA genes of A/Fiji together into clone 7a reduced apoptosis, whereas inserting clone 7a M, NA, and HA together into A/Fiji increased apoptosis. These results suggest that no single virus protein induces apoptosis and that the combination of genes required may be strain specific, highlighting the difficulty of predicting the virulence of new strains that arise in nature. No support for the view that apoptosis is essential for high virus yields was obtained as high virus yields were obtained with viruses that induced both high and low levels of apoptosis.

Amino Acid Sequence↗
PubMed2002

When reverse genetics meets physiology: the use of site-specific recombinases in mice.

The use of site-specific recombinases enables the precise introduction of defined genetic mutations into the mouse genome. In theory, any deletion, point mutation, inversion or translocation can be modeled in mice. Because gene targeting is controlled both spatially and temporally, the function of a given gene can be studied in the desired cell types and at a specific time point. This 'genetic dissection' allows to define gene function in development, physiology or behavior. In this review, we focus on the technical possibilities of Cre and other site-specific recombinases but also discuss their limitations.

Animals↗