Codons and hypercycles.

M Ycas

doi:10.1023/a:1006549309688

Home/Archive/PubMed

PubMed · 10077870

Codons and hypercycles.

M Ycas

View original source ↗Export metadata ↓

Abstract

Several hypotheses on the origin of codon assignments imply that the present protein synthesizing machinery was already in place when the assignments were made. These are examined by computer modeling. The results do not suggest that assignments were optimized for resistance to reading and mutation errors, nor that the assignments are random. It is improbable that the number of species of amino acids increased in the course of evolution. An originally ambiguous dictionary is likely to have been subject to error catastrophe and is improbable. A relation between amino acid properties and their codons exists, and suggests that the codon assignments were established at the time of origin of the hypercycle, i.e. a system of aminoacyl synthetases which attaches amino acids to tRNA, and before the present protein synthesizing machinery was in place. The origin of a hypercycle is only possible if the system began with components which were catalytically active even when they did not form a self-replicating system. A model of such a system is proposed.

Explore related subjects

Amino Acids Codon Computer Simulation Models, Genetic Journal Article Review

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

M Ycas. 1999. Codons and hypercycles.. https://doi.org/10.1023/a%3A1006549309688

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed2026

Chimeric structural isomer fragments as cost-efficient internal standards for amino acid quantification by mass spectrometry.

Amino acid (AA) profiles from body fluids such as blood and urine are clinical indicators for diagnosing metabolic and hepatic diseases. Current quantitative methods, such as liquid chromatography-mass spectrometry (LC-MS) with isotopically labelled internal standards (ISs), are costly and technically demanding. This study proposes a cost-efficient alternative using structural isomers as ISs in a direct liquid infusion (DLI) tandem mass spectrometry (MS/MS) approach. The method leverages chimeric spectra and fragment intensity ratios to quantify AAs, demonstrating high linearity and precision even with a 3D ion trap mass analyser. This approach offers a viable strategy for AA quantification in preventive medicine, particularly for screening metabolic diseases such as phenylketonuria, diabetes, and liver dysfunction.

Amino Acids↗

PubMed2001

Residue frequencies and pairing preferences at protein-protein interfaces.

We used a nonredundant set of 621 protein-protein interfaces of known high-resolution structure to derive residue composition and residue-residue contact preferences. The residue composition at the interfaces, in entire proteins and in whole genomes correlates well, indicating the statistical strength of the data set. Differences between amino acid distributions were observed for interfaces with buried surface area of less than 1,000 A(2) versus interfaces with area of more than 5,000 A(2). Hydrophobic residues were abundant in large interfaces while polar residues were more abundant in small interfaces. The largest residue-residue preferences at the interface were recorded for interactions between pairs of large hydrophobic residues, such as Trp and Leu, and the smallest preferences for pairs of small residues, such as Gly and Ala. On average, contacts between pairs of hydrophobic and polar residues were unfavorable, and the charged residues tended to pair subject to charge complementarity, in agreement with previous reports. A bootstrap procedure, lacking from previous studies, was used for error estimation. It showed that the statistical errors in the set of pairing preferences are generally small; the average standard error is approximately 0.2, i.e., about 8% of the average value of the pairwise index (2.9). However, for a few pairs (e.g., Ser-Ser and Glu-Asp) the standard error is larger in magnitude than the pairing index, which makes it impossible to tell whether contact formation is favorable or unfavorable. The results are interpreted using physicochemical factors and their implications for the energetics of complex formation and for protein docking are discussed. Proteins 2001;43:89-102.

Amino Acids↗

PubMed2001

Roles of amino acid residues near the chromophore of photoactive yellow protein.

To investigate the roles of amino acid residues around the chromophore in photoactive yellow protein (PYP), new mutants, Y42A, E46A, and T50A were prepared. Their spectroscopic properties were compared with those of wild-type, Y42F, E46Q, T50V, R52Q, and E46Q/T50V, which were previously prepared and specified. The absorption maxima of Y42A, E46A, and T50A were observed at 438, 469, and 454 nm, respectively. The results of pH titration for the chromophore demonstrated that the chromophore of PYP mutant, like the wild-type, was protonated and bleached under acidic conditions. The red-shifts of the absorption maxima in mutants tended toward a pK(a) increase. Mutation at Glu46 induced remarkable shifts in the absorption maxima and pK(a). The extinction coefficients were increased in proportion to the absorption maxima, whereas the oscillator strengths were constant. PYP mutants that conserved Tyr42 were in the pH-dependent equilibrium between two states (yellow and colorless forms). However, Y42A and Y42F were in the pH-independent equilibrium between additional intermediate state(s) at around neutral pH, in which yellow form was dominant in Y42F whereas the other was dominant in Y42A. These findings suggest that Tyr42 acts as the hinge of the protein, and the bulk as well as the hydroxyl group of Tyr42 controls the protein conformation. In all mutants, absorbance at 450 nm was decreased upon flash irradiation and afterwards recovered on a millisecond time scale. However, absorbance at 340--370 nm was increased vice versa, indicating that the long-lived near-UV intermediates are formed from mutants, as in the case of wild-type. The lifetime changes with mutation suggest the regulation of proton movement through a hydrogen-bonding network.

Amino Acids↗