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J L Chastain

Publications and source records attributed to J L Chastain.

8 recordsLinked to original sources
PubMed1995

Translational suppression by trinucleotide repeat expansion at FMR1.

Fragile X syndrome is the result of the unstable expansion of a trinucleotide repeat in the 5'-untranslated region of the FMR1 gene. Fibroblast subclones from a mildly affected patient, each containing stable FMR1 alleles with 57 to 285 CGG repeats, were shown to exhibit normal steady-state levels of FMR1 messenger RNA. However, FMR protein was markedly diminished from transcript with more than 200 repeats. Such transcripts were associated with stalled 40S ribosomal subunits. These results suggest that a structural RNA transition beyond 200 repeats impedes the linear 40S migration along the 5'-untranslated region. This results in translational inhibition by trinucleotide repeat expansion.

Centrifugation, Density Gradient↗
PubMed1992

Human genes containing polymorphic trinucleotide repeats.

Expansions of trinucleotide repeats within gene transcripts are responsible for fragile X syndrome, myotonic dystrophy and spinal and bulbar muscular atrophy. To identify other human genes with similar features as candidates for triplet repeat expansion mutations, we screened human cDNA libraries with repeat probes and searched databases for transcribed genes with repeats. From both strategies, 40 genes were identified and 14 characterized. Five were found to contain repeats which are highly polymorphic including the N-cadherin, BCR, glutathione-S-transferase and Na+/K+ ATPase (beta-subunit) genes. These data demonstrate the occurrence of other human loci which may undergo this novel mechanism of mutagenesis giving rise to genetic disease.

Base Sequence↗
PubMed1991

Abnormalities in protein synthesis and degradation induced by extracellular pH in BC3H1 myocytes.

Metabolic acidosis impairs protein and amino acid metabolism in rat muscle. To examine how extracellular acidification affects cellular protein turnover, we studied the BC3H1 myocyte. At pH 7.1 vs. 7.4, intracellular pH was lower; the decrease was greater in cells incubated in N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-tris(hydroxymethyl)aminomethane compared with bicarbonate buffer. We monitored degradation of proteins labeled with L-[14C]phenylalanine by measuring radioactivity released into media containing an excess of unlabeled phenylalanine. Extracellular acidification increased degradation compared with incubation at pH 7.4. Adding a physiological concentration of insulin (1 nM) decreased protein degradation at pH 7.1 and 7.4; a supraphysiological (71 nM) insulin concentration decreased degradation at pH 7.1 to the same rate as cells incubated at pH 7.4 without insulin. Compared with pH 7.4, protein synthesis decreased 29% at pH 7.2; at pH 7.6 it increased 129%. Insulin stimulated protein synthesis at all pHs, but at pH 7.4 the insulin-induced increase was less than the rate at pH 7.6 without insulin. Dexamethasone did not change protein breakdown regardless of the pH; it had variable effects on protein synthesis. Thus extracellular acidification causes marked changes in protein turnover in BC3H1 myocytes.

Acidosis↗
PubMed1988

Characterization of a new flavin metabolite from human urine.

A new flavin metabolite comprising approximately 5% of the total flavin of human urine was isolated and characterized using absorption and fluorescence spectra, oxidation-reduction and hydrolysis data, and ninhydrin reactions. The flavin is a derivative associated with a peptide residue in ester linkage from an amino acid carboxyl to the ribityl chain of riboflavin, probably at the 5'-terminus.

Adult↗
PubMed1987

Flavin catabolites: identification and quantitation in human urine.

Riboflavin is the primary flavin excreted in human urine but significant amounts of 7 alpha-hydroxyriboflavin and lesser amounts of 8 alpha-hydroxyriboflavin are present and reflect tissue microsomal oxidations. A newly found flavin catabolite of an 8 alpha-sulfonyl type may reflect intake and/or turnover of such thioether-linked flavin as occurs in monoamine oxidase. Additionally, lesser amounts of 10-hydroxyethylflavin (indicative of intestinal microbial action on the vitamin) and traces of lumiflavin (arising from photodecomposition) constitute part of the remaining flavin, which acutely reflects level of intake.

Adult↗
PubMed1987

Clarification and quantitation of primary (tissue) and secondary (microbial) catabolites of riboflavin that are excreted in mammalian (rat) urine.

Riboflavin derivatives were quantitated and identified in urine of rats fed 0, 2 and 6 micrograms riboflavin/g diet per day both with and without added succinyl sulfathiazole for 6 wk. Two rats from each dietary group were placed in metabolic cages and urine was collected in the dark for 24 h. On the fourth week, a third animal from each group received an i.p. injection of [2-14C]riboflavin before being placed in a metabolic cage and urine collected in the dark for 48 h. Urine samples were extracted with phenol for flavin components and with chloroform for lumichrome and derivatives. Riboflavin was the predominant flavin excreted by rats in all dietary groups, followed by hydroxymethylriboflavins and smaller amounts of flavin mononucleotide (FMN), lumiflavin and 10-hydroxyethylflavin. Carboxylumichromes accounted for 5-10% of the total flavin-derived fluorescence in urine of rats fed 2 and 6 micrograms riboflavin/g diet and were reduced to approximately 3% when sulfathiazole was added to the base diets. Carboxylumichromes were absent from urine of riboflavin-deficient rats. Riboflavin accounted for 85-90% of the recovered radioactivity of all radioactive urine extracts; no radioactively labeled carboxylumichromes were detected. These results indicate that hydroxymethylriboflavins are primary catabolites of riboflavin derived from tissue microsomal oxidations, whereas carboxylumichromes reflect the continued oxidation of ring hydroxymethyl functions plus gut microbial cleavage of the side chain of flavin.

Animals↗
PubMed1985

High-performance liquid chromatography of biotin and analogues.

Biotin, analogues, and chemical intermediates were separated by high-performance liquid chromatography (HPLC) using reversed-phase and anion-exchange chromatographic conditions. Reversed-phase separations provided a wide range of retention times and resolution of nearly all the biotin compounds from mixtures of the analogues. Anion-exchange separations gave generally shorter retention times as compared to reversed-phase separations and greater resolution between biotin l- and d-sulfoxide. However, fewer analogues were resolved from mixtures of the compounds with anion-exchange HPLC.

Biotin↗