Search PubMed⌕ Search

Biomedical subjects

E L Christian

Publications and source records attributed to E L Christian.

4 recordsLinked to original sources
PubMed1992

Analysis of the role of phosphate oxygens in the group I intron from Tetrahymena.

We have developed a quantitative substitution interference technique to examine the role of Pro-Rp oxygens in the phosphodiester backbone of RNA, using phosphorothioates as a structural probe. This approach is generally applicable to any reaction involving RNA in which the precursor and reaction products can be separated. We have applied the technique to identity structural requirements in the group I intron from Tetrahymena thermophila for catalysis of hydrolysis at the 3' splice site; 44 phosphate oxygens are important in 3' splice site hydrolysis. These include four or five oxygens previously observed to be important in exon ligation. Although phosphate oxygens having a functional significance can be found throughout the intron, the strongest phosphorothioate effects are closely associated with positions in the highly conserved intron core, which are likely to be involved in tertiary interactions, substrate recognition and catalysis.

Animals↗
PubMed1989

Stereoselective arginine binding is a phylogenetically conserved property of group I self-splicing RNAs.

We have examined the reaction of GTP with RNA polymerase transcripts containing the self-splicing RNA precursors from the Neurospora crassa Cob1 intron, and from introns in the sunY, nrdB and td genes of bacteriophage T4. In each case, we find a low Km for GTP (between 0.8 and 11 microM), accompanied by competitive inhibition of the GTP reaction by L-arginine, as was found for the previously examined Tetrahymena nuclear pre-rRNA intron. Trials with the 20 standard amino acids show that inhibition in all cases is specific to the arginine side-chain. L-arginine binds with similar affinity to all introns studied, the Ki's ranging from 4.3 to 21 mM. Strikingly, the relative binding preference of the RNAs for L- versus D-arginine is highly conserved: the ratio of L-arg Ki/D-arg Ki, the stereoselectivity, is always close to 2. Because of the conservation of GTP and arginine binding constants and particularly because of the conserved stereoselectivity, we conclude that the evolution of an effective group I RNA transesterification catalyst necessarily produces a specific and stereoselective RNA binding site for a single amino acid. This suggests that selection for an ancient group I RNA could have fortuitously initiated the specific association of RNA sequences with amino acids, a first step toward the genetic code.

Amino Acids↗
PubMed1989

Epidermal growth factor immunoreactive material in the rat brain. Localization and identification of multiple species.

Brains of adult male rats were dissected into five distinct regions: brainstem, cerebellum, hippocampus, diencephalon, and telencephalon. Epidermal growth factor-like immunoreactivity was isolated and characterized by radioimmunoassay and nondenaturing polyacrylamide gel electrophoresis. Radioimmunoassay indicated levels of standard rat epidermal growth factor equivalents ranging from 0.99 to 0.33 ng/g wet weight of brain tissue. Competition curves were not parallel to those generated with standard rat epidermal growth factor, indicating a lack of structural identity between the immunoreactive material in the brain and standard rat epidermal growth factor. Extracts of submandibular gland and blood did, however, produce parallel competition curves. Electrophoresis indicated the presence of multiple bands of immunoreactive material in each of the regions of the brain. The major bands of activity migrated to positions distinct from that of standard rat epidermal growth factor. This is the first demonstration of multiple forms of epidermal growth factor-like immunoreactive material in the central nervous system.

Animals↗