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Results for “genetic code change”

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At least 397 records · Page 22Linked to original sources
PubMed2006

Transformation of the green alga Haematococcus pluvialis with a phytoene desaturase for accelerated astaxanthin biosynthesis.

Astaxanthin is a high-value carotenoid which is used as a pigmentation source in fish aquaculture. Additionally, a beneficial role of astaxanthin as a food supplement for humans has been suggested. The unicellular alga Haematococcus pluvialis is a suitable biological source for astaxanthin production. In the context of the strong biotechnological relevance of H. pluvialis, we developed a genetic transformation protocol for metabolic engineering of this green alga. First, the gene coding for the carotenoid biosynthesis enzyme phytoene desaturase was isolated from H. pluvialis and modified by site-directed mutagenesis, changing the leucine codon at position 504 to an arginine codon. In an in vitro assay, the modified phytoene desaturase was still active in conversion of phytoene to zeta-carotene and exhibited 43-fold-higher resistance to the bleaching herbicide norflurazon. Upon biolistic transformation using the modified phytoene desaturase gene as a reporter and selection with norflurazon, integration into the nuclear genome of H. pluvialis and phytoene desaturase gene and protein expression were demonstrated by Southern, Northern, and Western blotting, respectively, in 11 transformants. Some of the transformants had a higher carotenoid content in the green state, which correlated with increased nonphotochemical quenching. This measurement of chlorophyll fluorescence can be used as a screening procedure for stable transformants. Stress induction of astaxanthin biosynthesis by high light showed that there was accelerated accumulation of astaxanthin in one of the transformants compared to the accumulation in the wild type. Our results strongly indicate that the modified phytoene desaturase gene is a useful tool for genetic engineering of carotenoid biosynthesis in H. pluvialis.

Biotechnology↗
PubMed1987

Evolution of genes for allelic and isotypic forms of immunoglobulin kappa chains and of the genes for T-cell receptor beta chains in rabbits.

New insights into the evolution of the families of genes encoding immunoglobulins and T-cell receptors of rabbits (Oryctolagus cuniculus) have come from molecular genetic studies. In contrast to human and mouse, rabbits were shown to have two genes for the constant region of immunoglobulin light chains (C kappa 1 and C kappa 2 isotypes) and complex allelic variants of K1 (allotypes). Although K1 allotype protein sequences differed at up to 41% of the amino acid positions, 3' untranslated, 5', and 3' flanking regions were conserved, and in the coding regions 78-80% of the codons with differences had replacement changes. Proportions of silent changes and changes in noncoding regions were comparable. Thus, in spite of their markedly different protein sequences, the K1b4, b5, and b9 allotypes appeared to be products of allelic genes. Molecular genetic analyses suggested that they may have undergone rapid divergence after an ancestral K2-like gene duplicated. Some rabbits were found to have two similar T-cell receptor C beta genes as do humans and many strains of mice, but others appeared to have three different C beta. In addition, we found allotypic forms of C beta. Some of the C beta allotypic differences occurred at positions where analogous C kappa allotypic differences were found. We also found V beta in mouse and human that were more similar to rabbit V beta than closely linked rabbit genes were to each other. This contrasts with rabbit immunoglobulin VH gene sequences that reflect concerted evolution. The data suggested that T-cell receptor V beta genes duplicated prior to mammalian radiation.

Alleles↗
PubMed2000

The CART gene and human obesity: mutational analysis and population genetics.

The cocaine- and amphetamine-regulated transcript (CART) peptide is a recently characterized neuropeptide implicated in the control of appetite. We hypothesized that genetic variation in CART may contribute to human obesity. The entire coding region of CART was determined by nucleotide sequencing in 91 unrelated subjects with severe early-onset obesity. A novel amino acid change, Ser66Thr, was found in 2 probands and in 0 of 100 control subjects but did not cosegregate with obesity in family studies. Two common polymorphisms were found in the 3'-untranslated region (A1475G and deltaA1457). An effect of these polymorphisms on body composition and intermediate phenotypes related to obesity was examined in a large Caucasian population in the U.K. Neither polymorphism showed any significant relationship with obesity; however, men heterozygous for the A1475G variant had significantly lower waist-to-hip ratio (WHR), fasting plasma insulin, and fasting triglycerides. Regression analysis indicated that the effects on insulin and triglycerides were likely to be secondary to the effects on WHR. Thus, we have conducted the first systematic study of the CART gene in human obesity, and although no clear association with obesity was found, the data suggest that genetic variation in the CART locus might influence fat distribution and variables related to syndrome X.

3' Untranslated Regions↗
PubMed2001

Genetics of the epilepsies.

Recent molecular insights into the human idiopathic epilepsies have suggested the central role of ligand-gated and voltage-gated ion channels in their etiology. So far, genes coding for sodium and potassium channel subunits as well as a nicotinic cholinergic receptor subunit have been identified for mendelian idiopathic epilepsies. In vitro and in vivo studies of mutations demonstrate functional changes, allowing new insights into mechanisms underlying hyperexcitability. Similarly, spontaneous murine epilepsy models have been associated with calcium channel molecular defects. The major challenge before us in understanding the genetics of the epilepsies is to identify genes for common forms of epilepsy following complex inheritance. Once such genes are discovered, the gene-gene-environmental interactions producing specific epilepsy syndromes can be explored.

Animals↗
PubMed2000

Genetics of the epilepsies.

Recent molecular insights into the human idiopathic epilepsies have suggested the central role of ligand-gated and voltage-gated ion channels in their etiology. So far, genes coding for sodium and potassium channel subunits as well as a nicotinic cholinergic receptor subunit have been identified for Mendelian idiopathic epilepsies. In vitro and in vivo studies of mutations demonstrate functional changes, allowing new insights in mechanisms underlying hyperexcitability. Similarly, spontaneous murine epilepsy models have been associated with calcium channel molecular defects. The major challenge before us in understanding the genetics of the epilepsies is to identify genes for common forms of epilepsy following complex inheritance. Once such genes are discovered, the gene-gene-environmental interactions producing specific epilepsy syndromes can be explored.

Epilepsy↗
PubMed1986

Actin and myosin multigene families: their expression during the formation and maturation of striated muscle.

The initial formation of skeletal muscle fibers is accompanied by the expression of muscle-type actin and myosin genes. During subsequent maturation of muscle fibers in vivo, developmental changes in the fetal/adult isoforms of these proteins occur. Skeletal muscle-specific transcripts coding for different myosin heavy chains accumulate sequentially both in vivo and in vitro. A genetic analysis demonstrates that these genes are clustered, implicating cis-acting regulatory factors. In contrast, actin and myosin light chain genes are dispersed in the mouse genome. These gene families show a different developmental "strategy": Genes expressed in adult cardiac tissue are coexpressed with the corresponding skeletal muscle sequence during fetal development. This phenomenon also occurs in adult tissue. Under conditions of cardiac overload, adult rat hearts accumulate skeletal actin mRNA and cardiac actin transcripts. In some mouse lines, a mutant cardiac actin gene locus is present. The presence of a second active upstream promoter at this locus depresses transcription of the bone fide gene, resulting in low levels of mature cardiac actin mRNA. In this situation skeletal actin gene transcripts accumulate. Genes expressed in the same fetal or adult muscle phenotype are not linked, suggesting that their coexpression is regulated by transacting factors. The promoter regions of such genes in the mouse have no common characteristics of primary structure with the exception of an E1A-type enhancer core sequence, which has a conserved 5' flanking element, seen for actin and myosin light chain genes. Reintroduction of these promoter regions into muscle cells provides a functional test for such potential regulatory sequences.

Actins↗
PubMed1992

Molecular polymorphisms of house dust mite allergens.

Previous studies from this laboratory have described the primary amino acid sequences of the group I and group II allergens from Dermatophagoides pteronyssinus and D. farinae. This report concentrates on polymorphisms of allergens within a species. Firstly, four cDNA clones of Der fII produced by polymerase chain reaction have been sequenced and are compared to the sequences published previously by ourselves and others. Although the sequences come from different sources, Australia and Japan, the overriding conclusion is one of similarity, with only two possible non-conservative changes in the six sequences. The nucleotides were also very conserved including the 3' untranslated regions, although some non-coding differences could be found which may provide a genetic marker. Experiments are reported to help define the group III D. pteronyssinus allergens. Previous studies have characterised the group III of D. farinae as a Mr 29-kDa molecule which can be defined by monoclonal antibodies. A Mr 17-kDa molecule of D. pteronyssinus has been reported with an almost identical N-terminal sequence. Here it is described that Der fIII isolated from different preparations of spent mite media by affinity chromatography have predominantly Mr 32-, 28- and 21-kDa forms which vary in degree from batch to batch. 83% of adults and 38% of children react with the preparation by radioimmune dot-blot. The difference between the children and adults is statistically significant and reactivity can be to at least the 32- and 28-kDa form. Antisera produced in mice against the Der fIII react to D. pteronyssinus mite extract by Western blotting primarily to a 32-kDa moiety, but also 28- and 21-kDa forms in some extracts.

Allergens↗
PubMed2000

Assignment of a form of congenital muscular dystrophy with secondary merosin deficiency to chromosome 1q42.

We have previously reported an autosomal recessive form of congenital muscular dystrophy, characterized by proximal girdle weakness, generalized muscle hypertrophy, rigidity of the spine, and contractures of the tendo Achilles, in a consanguineous family from the United Arab Emirates. Early respiratory failure resulting from severe diaphragmatic involvement was present. Intellect and the results of brain imaging were normal. Serum creatine kinase levels were grossly elevated, and muscle-biopsy samples showed dystrophic changes. The expression of the laminin-alpha2 chain of merosin was reduced on several fibers, but linkage analysis excluded the LAMA2 locus on chromosome 6q22-23. Here, we report the results of genomewide linkage analysis of this family, by use of homozygosity mapping. In all four affected children, an identical homozygous region was identified on chromosome 1q42, spanning 6-15 cM between flanking markers D1S2860 and D1S2800. We have identified a second German family with two affected children having similar clinical and histopathological features; they are consistent with linkage to the same locus. The cumulative LOD score was 3.57 (straight theta=.00) at marker D1S213. This represents a novel locus for congenital muscular dystrophy. We suggest calling this disorder "CMD1B." The expression of three functional candidate genes in the CMD1B critical region was investigated, and no detectable changes in their level of expression were observed. The secondary reduction in laminin-alpha2 chain in these families suggests that the primary genetic defect resides in a gene coding for a protein involved in basal lamina assembly.

Antigens, CD↗
PubMed1996

Genetic analysis of second primary lung cancers in patients surviving small cell lung cancer.

We performed genetic analysis on 12 second primary non-small cell lung cancers in patients surviving small cell lung cancer to assess the potential contribution of smoking to the development of these tumors. Mutations of TP53 were found in three (25%) tumors, KRAS2 in three (25%) tumors, and CDKN2 in two (18%) tumors. Four (50%) mutations (one each in TP53 and CDKN2 and two in KRAS2) were G:C to T:A transversions on the coding strand, a mutation accounting for approximately one-third of mutations in smoking-related tumors but uncommonly found in lung cancers not associated with smoking. The genetic changes in these second lung cancers are more representative of smoking-associated malignancies than lung cancers arising in patients occupationally exposed to irradiation and atomic bomb survivors.

Carcinoma, Small Cell↗
PubMed2002

The molecular genetics of the human I locus and molecular background explain the partial association of the adult i phenotype with congenital cataracts.

The human i and I antigens are characterized as linear and branched repeats of N-acetyllactosamine, respectively. Conversion of the i to the I structure requires I-branching beta-1,6-N-acetylglucosaminyltransferase activity. It has been noted that the null phenotype of I, the adult i phenotype, is associated with congenital cataracts in Asians. Previously, the identification of molecular changes in the IGnT gene, associated with the adult i phenotype, has been reported. In the present study, we demonstrate that the human I locus expresses 3 IGnT forms, designated IGnTA, IGnTB, and IGnTC, which have different exon 1, but identical exons 2 and 3, coding regions. The molecular genetics proposed for the I locus offer a new perspective on the formation and expression of the I antigen in different cells and provide insight into the questions derived from investigation of the adult i phenotype. Molecular genetic analyses of the I loci of the 2 adult i groups, with and without congenital cataracts, were performed, and enzyme function assays and expression patterns for the 3 IGnT transcripts in reticulocytes and lens-epithelium cells were analyzed. The results suggest a molecular genetic mechanism that may explain the partial association of the adult i phenotype with congenital cataracts and indicate that a defect in the I locus may lead directly to the development of congenital cataracts. The results also suggest that the human blood group I gene should be reassigned to the IGnTC form, not the IGnTB form, as described previously.

Adult↗
PubMed1989

Evolution of the mitochondrial genetic code. II. Reassignment of codon AUA from isoleucine to methionine.

The reassignment of codon AUA from isoleucine to methionine during mitochondrial evolution may be explained by the codon reassignment (capture) hypothesis without assuming direct replacement of isoleucine by methionine in mitochondrial proteins. According to this hypothesis, codon AUA would have disappeared from the reading frames of messenger RNA. AUA codons would have mutated mainly to AUU isoleucine codons because of constraints resulting from elimination of tRNA Ile with anticodon *CAU (in which *C is lysidine). Later, tRNA Met (CAU) would have undergone structural changes enabling it to pair with both AUG and AUA. AUA codons, formed by mutations of other codons, including AUG, would have reappeared and would have been translated as methionine.

Animals↗
PubMed2005

West Nile virus in host-seeking mosquitoes within a residential neighborhood in Grand Forks, North Dakota.

West Nile virus (WNV) was first recovered in North Dakota near the city of Grand Forks in June 2002. During 2002, 2003, and 2004, we collected mosquitoes from Grand Forks using Mosquito Magnet traps and tested them for WNV. The seasonal abundance, species composition, and reproductive status of female mosquitoes were correlated with local environmental temperature and state surveillance data on WNV to determine the factors affecting local transmission of WNV. Over 90% of the mosquitoes collected were Aedes vexans, Ochlerotatus dorsalis, and Culex tarsalis, but WNV was detected only in Cx. tarsalis. Average summertime temperatures and relative abundance of mosquitoes were highest in 2002 but no WNV-positive mosquitoes were detected until the following summer. In 2003, nulliparous Cx. tarsalis appeared in mid-June (first summer brood), and parous Cx. tarsalis appeared in mid-July. The first WNV-positive pool occurred 21 July, and minimum daily infections rates increased thereafter until 27 August. The minimum infection rate (MIR) for Cx. tarsalis during the season was 5.7 infected mosquitoes per 1,000 tested, with the highest infection rates occurring at the end of the season as Cx. tarsalis populations started to decline. Mid-to-late August was identified as the period of highest risk for being bitten by a WNV-infected mosquito in Grand Forks during 2003. In 2004, viral activity in Grand Forks was low, due to very cool temperatures throughout the summer. To examine the genetic diversity of the 2003 WNV isolates from Grand Forks, we sequenced a 366-nucleotide region of the capsid and premembrane gene. Thirteen (46%) of the 28 WNV isolates contained at least one nucleotide substitution when compared to the homologous region of the progenitor WN NY-99 strain, and seven of these 13 substitutions coded for amino acid changes. Thus, WNV is established in North Dakota, it appears to be evolving and it is vectored primarily by Cx. tarsalis.

Aedes↗
PubMedDate not supplied

Isolation and expression of two genes encoding eukaryotic release factor 1 from Paramecium tetraurelia.

Paramecium tetraurelia, like some other ciliate species, uses an alternative nuclear genetic code where UAA and UAG are translated as glutamine and UGA is the only stop codon. It has been postulated that the use of stop codons as sense codons is dependent on the presence of specific tRNAs and on modification of eukaryotic release factor one (eRF1), a factor involved in stop codon recognition during translation termination. We describe here the isolation and characterisation of two genes, eRF1-a and eRF1 b, coding for eRF1 in P. tetraurelia. The two genes are very similar, both in genomic organization and in sequence, and might result from a recent duplication event. The two coding sequences are 1,314 nucleotides long, and encode two putative proteins of 437 amino acids with 98.5% identity. Interestingly, when compared with the eRF1 sequences either of ciliates having the same variant genetic code, or of other eukaryotes, the eRF1 of P. tetraurelia exhibits significant differences in the N-terminal region, which is thought to interact with stop codons. We discuss here the consequences of these changes in the light of recent models proposed to explain the mechanism of stop codon recognition in eukaryotes. Besides, analysis of the expression of the two genes by Northern blotting and primer extension reveals that these genes exhibit a differential expression during vegetative growth and autogamy.

Amino Acid Sequence↗
PubMed1984

Oncogenes and human cancer.

In the past, the investigation of the causes of cancer has seemed to involve many unconnected disciplines such as tumour virology, chemical carcinogenesis, and chromosomal analysis. Oncogene research has revealed exciting links between these, and the identification of some of the biochemical mechanisms associated with malignant change offers hope for the development of more specific therapies.

Animals↗
PubMed2006

Targeting DNA methylation in cancer.

Cancer growth and metastasis require the coordinate change in gene expression of different sets of genes. While genetic alterations can account for some of these changes, many of the changes in gene expression observed in cancer are caused by epigenetic modifications. The epigenome consists of the chromatin and its modifications, the "histone code" as well as the pattern of distribution of covalent modifications of cytosines residing in the dinucleotide sequence CG by methylation. The normal pattern of distribution of DNA methylation is altered in cancer. A number of genes are regionally hypermethylated but many parts of the genome are hypomethylated. Hypermethylation of tumor suppressor genes is involved in silencing of strategic genes. DNA hypermethylation has received much attention and a number of clinical trials are underway with different inhibitors of DNA methylating enzymes. It is now becoming clear however that hypomethylation also plays a role in cancer by activating genes required for invasion and metastasis. The potential therapeutic implications of targeting DNA methylation in cancer are discussed.

Acetylation↗
PubMed2004

Probing the role of tryptophans in Aequorea victoria green fluorescent proteins with an expanded genetic code.

The expanded genetic code in combination with site-directed mutagenesis was used to probe spectroscopic and structural roles of tryptophan (Trp) residues in Aequorea victoria green fluorescent proteins (avGFPs). Nine different halogen-, chalcogen-, and methyl-containing Trp isosteric analogues and surrogates were incorporated into avGFPs containing indole moieties in, and outside of, the chromophore, by the use of the selective pressure incorporation method. Such isosteric replacements introduced minimal local geometry changes in indole moieties, often to the level of single atomic exchange ('atomic mutation') and do not affect three-dimensional structures of avGFPs but induce changes in spectral properties. Our approach offers a new platform to re-evaluate issues like resonance transfer, mechanisms of chromophore formation and maturation, as well as the importance of local geometry and weak sulphur-aromatic interactions for avGFP spectral properties and structural stability. The library of novel tailor-made avGFP mutants and variants generated in this work has demonstrated not only the potentials of the expanded genetic code to study spectroscopic functions, but also a new approach to generate tailor-made proteins with interesting and useful spectral properties.

Aequorin↗