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The chromosome end in yeast: its mosaic nature and influence on recombinational dynamics.

ABSTRACT: Yeast chromosome ends are composed of several different repeated elements. Among six clones of chromosome ends from two strains of Saccharomyces cerevisiae, at least seven different repeated sequence families were found. These included the previously identified Y' and X elements. Some families are highly variable in copy number and location between strains of S. cerevisiae, while other elements appear constant in copy number and location. Three repeated sequence elements are specific to S. cerevisiae and are not found in its evolutionarily close relative, Saccharomyces paradoxus. Two other repeated sequences are found in both S. cerevisiae and S. paradoxus. None of those described here is found (by low stringency DNA hybridization) in the next closest species, Saccharomyces bayanus. The loosely characterized X element is now more precisely defined. X is a composite of at least four small (ca. 45-140 bp) sequences found at some, but not all, ends. There is also a potential "core" X element of approximately 560 bp which may be found at all ends. Distal to X, only one of six clones had (TG1-3)n telomere sequence at the junction between X and Y'. The presence of these internal (TG1-3)n sequences correlates with the ability of a single Y' to expand into a tandem array of Y's by unequal sister chromatid exchange. The presence of shared repeated elements proximal to the X region can override the strong preference of Y's to recombine ectopically with other Y's of the same size class. The chromosome ends in yeast are evolutionarily dynamic in terms of subtelomeric repeat structure and variability.

SUBMITTER: Louis EJ

PROVIDER: S-EPMC1205885 | biostudies-other | 1994 Mar

REPOSITORIES: biostudies-other

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The chromosome end in yeast: its mosaic nature and influence on recombinational dynamics.

Louis E J EJ Naumova E S ES Lee A A Naumov G G Haber J E JE

Genetics 19940301 3

Yeast chromosome ends are composed of several different repeated elements. Among six clones of chromosome ends from two strains of Saccharomyces cerevisiae, at least seven different repeated sequence families were found. These included the previously identified Y' and X elements. Some families are highly variable in copy number and location between strains of S. cerevisiae, while other elements appear constant in copy number and location. Three repeated sequence elements are specific to S. cerev ...[more]

PMID: 8005434

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Project description:Modified nucleotides are prevalent in tRNA. Experimental studies reveal that these covalent modifications play an important role in tuning tRNA function. In this study, molecular dynamics (MD) simulations were used to investigate how modifications alter tRNA dynamics. The X-ray crystal structures of tRNA(Asp), tRNA(Phe), and tRNA(iMet), both with and without modifications, were used as initial structures for 333 ns explicit solvent MD simulations with AMBER. For each tRNA molecule, three independent trajectory calculations were performed, giving an aggregate of 6 ?s of total MD across six molecules. The global root-mean-square deviations (RMSD) of atomic positions show that modifications only introduce significant rigidity to the global structure of tRNA(Phe). Interestingly, RMSDs of the anticodon stem-loop (ASL) suggest that modified tRNA has a more rigid structure compared to the unmodified tRNA in this domain. The anticodon RMSDs of the modified tRNAs, however, are higher than those of corresponding unmodified tRNAs. These findings suggest that the rigidity of the anticodon stem-loop is finely tuned by modifications, where rigidity in the anticodon arm is essential for tRNA translocation in the ribosome, and flexibility of the anticodon is important for codon recognition. Sugar pucker and water residence time of pseudouridines in modified tRNAs and corresponding uridines in unmodified tRNAs were assessed, and the results reinforce that pseudouridine favors the 3'-endo conformation and has a higher tendency to interact with water. Principal component analysis (PCA) was used to examine correlated motions in tRNA. Additionally, covariance overlaps of PCAs were compared for trajectories of the same molecule and between trajectories of modified and unmodified tRNAs. The comparison suggests that modifications alter the correlated motions. For the anticodon bases, the extent of stacking was compared between modified and unmodified molecules, and only unmodified tRNA(Asp) has significantly higher percentage of stacking time. Overall, the simulations reveal that the effect of covalent modification on tRNA dynamics is not simple, with modifications increasing flexibility in some regions of the structure and increasing rigidity in other regions.

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The chromosome end in yeast: its mosaic nature and influence on recombinational dynamics.

Publications

The chromosome end in yeast: its mosaic nature and influence on recombinational dynamics.

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