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PubMedDate not supplied

Drosophila melanogaster mitochondrial DNA, a novel organization and genetic code.

The sequence of a 4,869 base-pair fragment of Drosophila melanogaster mitochondrial DNA is presented. It contains genes for cytochrome oxidase subunits I, II and III, ATPase subunit 6 and six tRNAs together with two unassigned reading frames. The gene organization differs from that of mammalian mitochondrial DNAs. Evidence is provided for a genetic code in which AGA codes for serine and the quadruplet ATAA is used in initiation of translation.

Amino Acid Sequence↗

PubMed2004

Modulation of base-specific mutation and recombination rates enables functional adaptation within the context of the genetic code.

The persistence of life requires populations to adapt at a rate commensurate with the dynamics of their environment. Successful populations that inhabit highly variable environments have evolved mechanisms to increase the likelihood of successful adaptation. We introduce a 64 x 64 matrix to quantify base-specific mutation potential, analyzing four different replicative systems, error-prone PCR, mouse antibodies, a nematode, and Drosophila. Mutational tendencies are correlated with the structural evolution of proteins. In systems under strong selective pressure, mutational biases are shown to favor the adaptive search of space, either by base mutation or by recombination. Such adaptability is discussed within the context of the genetic code at the levels of replication and codon usage.

Adaptation, Biological↗

PubMed1991

Selenoprotein synthesis: an expansion of the genetic code.

A number of enzymes employ the unusual amino acid selenocysteine as part of their active site because of its high chemical reactivity. Selenocysteine is incorporated into these proteins co-translationally: biosynthesis occurs on a specific tRNA and insertion into a growing polypeptide is directed by a UGA codon in the mRNA. In E. coli, this requires a specific translation factor. Selenocysteine thus represents a unique expansion of the genetic code.

Animals↗

PubMed1995

Direct interaction between amino acids and nucleotides as a possible physicochemical basis for the origin of the genetic code.

A study of the association of homocodonic amino acids and selected heterocodonic amino acids with selected nucleotides in aqueous solution was undertaken to examine a possible physical basis for the origin of codon assignments. These interactions were studied using 1H nuclear magnetic resonance spectroscopy (NMR). Association constants for the various interactions were determined by fitting the changes in the chemical shifts of the anomeric and ring protons of the nucleoside moieties as a function of amino acid concentration to an isotherm which described the binding interaction. The strongest association of all homocodonic amino acids were with their respective anticodonic nucleotide sequences. The strength of association was seen to increase with increase in the chain length of the anticodonic nucleotide. The association of these amino acids with different phosphate esters of nucleotides suggests that a definite isomeric structure is required for association with a specified amino acid; the 5'-mononucleotides and (3'-5')-linked dinucleotides are the favored geometries for strong associations. Use of heterocodonic amino acids and nonprotein amino acids supports these findings. We conclude that there is at least a physicochemical, anticodonic contribution to the origin of the genetic code.

Amino Acids↗

PubMed2006