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1.
Construction and expression of synthetic DNA fragments coding for polypeptides with elevated levels of essential amino acids 总被引:1,自引:0,他引:1
J. M. Jaynes P. Langridge K. Anderson C. Bond D. Sands C. W. Newman R. Newman 《Applied microbiology and biotechnology》1985,21(3-4):200-205
Summary Polypeptides, with elevated levels of essential amino acids, could be useful as partial protein supplements to food and feeds. To obtain DNA fragments coding for these polymers, oligonucleotides were constructed by random synthesis of a mixture of appropriate codon pairs and inserted into a bacterial plasmid in E. coli. Two of the isolated fragments were subjected to DNA sequence analysis and theoretically code for polypeptides containing up to 23% lysine, 12% tryptophan, 12% methionine, 6% isoleucine, and 6% threonine. These five amino acids make up 60% of the total amino acid content of the peptide, compared with 25% for the same amino acids in lactalbumin, a milk protein considered to be high in essential amino acids. These fragments, when fused to an active bacterial promoter, which directs the synthesis of chloramphenicol acetyl transferase (CAT), cause bacteria, harboring these modified genes, to take up more lysine as compared to control cells and produce commensurately larger CAT polypeptides. This method of gene synthesis may permit production of polypeptides with a specified amino acid composition to supplement specific diets low in the essential amino acids. 相似文献
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An invertase inactivator in maize endosperm and factors affecting inactivation 总被引:15,自引:10,他引:5 下载免费PDF全文
A protein present in the developing endosperm of maize (Zea mays L.) causes a loss of invertase activity under certain conditions of incubation. This protein, designated an inactivator, inactivates invertase I of maize even in the presence of other proteins. No inactivation of invertase II of maize or yeast invertase has been observed. The inactivator and invertase I are found only in the endosperm. The quantity of inactivator increases in the normal endosperm during development while invertase I activity decreases. However, the altered levels of invertase I activity in several endosperm mutant lines do not result from different quantities of inactivator. The inactivator can decrease invertase I activity during a preincubation period before addition of sucrose; inactivation is noncompetitive. Invertase I activity decreases curvilinearly with an increase in inactivator concentration. At high buffer concentrations or low inactivator concentrations in the reaction mixture, a latent period is observed when invertase I is not inactivated. Inactivation increases with an increase in temperature and a decrease in pH. 相似文献
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The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from
nucleotide sequence variation across a 765-bp region in the cytochrome
oxidase I and II genes of the mitochondrial genome. Most parsimonious
relationships of 25 haplotypes from 16 Greya species and two outgroup
genera (Tetragma and Prodoxus) showed substantial congruence with the
species relationships indicated by morphological variation. Differences
between mitochondrial and morphological trees were found primarily in the
positions of two species, G. variabilis and G. pectinifera, and in the
branching order of the three major species groups in the genus. Conflicts
between the data sets were examined by comparing levels of homoplasy in
characters supporting alternative hypotheses. The phylogeny of Greya
species suggests that host-plant association at the family level and larval
feeding mode are conservative characters. Transition/transversion ratios
estimated by reconstruction of nucleotide substitutions on the phylogeny
had a range of 2.0-9.3, when different subsets of the phylogeny were used.
The decline of this ratio with the increase in maximum sequence divergence
among taxa indicates that transitions are masked by transversions along
deeper internodes or long branches of the phylogeny. Among transitions,
substitutions of A-->G and T-->C outnumbered their reciprocal
substitutions by 2-6 times, presumably because of the approximately 4:1
(77%) A+T-bias in nucleotide base composition. Of all transversions,
73%-80% were A<-->T substitutions, 85% of which occurred at third
positions of codons; these estimates did not decrease with an increase in
maximum sequence divergence of taxa included in the analysis. The high
frequency of A<-->T substitutions is either a reflection or an
explanation of the 92% A+T bias at third codon positions.
相似文献
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Summary A membrane interactive peptide was toxic to microspores, pollen and protoplasts of canola in the 1–5 µM concentration range. Similarly, at 5.0 µM the peptide completely inhibited germination of conidia ofVerticillium albo-atrum; however, when tested with conidia of a virulent isolate of blackleg (Leptosphaeria maculens), a fungal pathogen of canola, much higher levels (>30 µM) of the peptide were required to reduce or arrest germination and growth of the conidia. When testing the relative toxicities of novel peptides on plant cells and their pathogens, pollen germination is a simple, rapid and reliable alternative to protoplasts. 相似文献
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Partial characterization of the plasma membrane ATPase from arho
0 petite strain ofSaccharomyces cerevisiae 总被引:2,自引:0,他引:2
James P. McDonough Patrick K. Jaynes Henry R. Mahler 《Journal of bioenergetics and biomembranes》1980,12(3-4):249-264
Crude membrane preparations of arho
0 mutant ofSaccharomyces cerevisiae exhibit Mg2+-dependent ATPase activity. Over the optimal pH range, 5.0–6.75, the apparentV
max of the enzyme equals 590 nmoles of ATP hydrolyzed per minute per milligram protein, with an apparentK
m
for ATP of 1.3 mM. ATP hydrolysis is insensitive to ouabain, venturicidin, aurovertin, and the protein inhibitor described by Pullman and Monroy; inhibited by oligomycin (at high concentrations) and sodium orthovandate, and it is sensitive to dicyclohexylcarbodiimide,p-hydroxymercuribenzoate, hydroxylamine, sodium fluoride, and sodium iodoacetate. The pH optimum and the inhibitor pattern distinguish the plasma membrane enzyme from the mitochondrial F1 ATPase still present in these cells (this activity is sensitive to efrapeptin, aurovertin, and the protein inhibitor, but resistant to DCCD). In addition, the activity of the plasma membrane enzyme and its affinity for ATP are responsive to changes in the composition of the growth medium, with the highest activity observed in cells grown on methyl--d-glucoside, a sugar which results not only in partial release from catabolite repression but also requires the induction of an active transport system for growth.Author to whom correspondence should be addressed; recipient of a Research Career Award No. K06 05060 from the Institute of General Medical Sciences. 相似文献
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