ABSTRACT
We have developed a computational method that detects 'identities' in tRNA genes by using principal component analysis to classify the sequences of bases in tRNA genes into groups of similar sequences and then comparing the distribution of sequences of bases, in order to extract characteristic bases that are conserved within a group but differ between groups. These classification and comparison procedures are applied recursively to classify the sequences into hierarchical groups, so that multiple levels of characteristic sites can be detected. By using this computational method, we were able to detect many characteristic sites in the T and D domains of tRNAs, as well as the characteristic sites that had already been detected experimentally. This suggests that bases not only in the contact regions but also in the elbow regions, which determine the structure and dynamics of the whole tRNA molecule, are important to the tRNA-aminoacyl tRNA synthetase recognition.
Subject(s)
Base Sequence , DNA, Bacterial/chemistry , DNA, Bacterial/genetics , RNA, Transfer/genetics , Amino Acyl-tRNA Synthetases/metabolism , Anticodon , Escherichia coli/genetics , Genes, Bacterial , Models, Molecular , Molecular Sequence Data , Nucleic Acid Conformation , RNA, Bacterial/genetics , RNA, Transfer, Gln/genetics , RNA, Transfer, Leu/genetics , RNA, Transfer, Pro/genetics , Sequence Alignment , Sequence Homology, Nucleic AcidABSTRACT
Glutathione levels in neurons and glial cells were investigated in a neuronal-glial coculture and in separate cultures. Brain cell suspensions obtained from cerebral hemispheres of fetal rats were cultured, and after 5 days the glutathione content of this cell population, consisting mainly of neurons and astroglial cells, was 23.0 nmol/mg of cell protein, with a significantly high content in glial cells (28.0 nmol/mg of protein) in comparison with neurons (18.8 nmol/mg of protein). When the neurons and glial cells were separated and recultured in fresh medium, neuronal glutathione rapidly decreased, whereas glial glutathione remained unchanged. Cysteine is a rate-limiting precursor for glutathione synthesis, and its level was also decreased in neurons, but not in glial cells. Cysteine was taken up rapidly by both neurons and glial cells, but cystine was taken up only by glial cells. This accounts for the rapid decrease of glutathione in the cultured neurons, because the culture medium contains cystine, but not cysteine. It was also found that the cultured glial cells released cysteine into the medium. These results suggest that neurons maintain their glutathione level by taking up cysteine provided by glial cells.
