Quantitation of mitochondrial DNA carrying tRNALys mutation in MERRF patients

An A to G transition at nucleotide position 8,344 in tRNALys of mitochondrial DNA has been recently identified as a causative mutation of myoclonus epilepsy associated with ragged-red fibers (MERRF). To investigate if the degree of heteroplasmy of mitochondrial DNA is correlated with the severity of MERRF, we have developed a novel method for quantitation of the mutant mitochondrial DNA by polymerase chain reaction using a mismatched primer. With the method, populations of mutant mtDNAs from 5 cases of MERRF carrying the tRNALys mutation were analyzed. The tight linkage of the severity of symptoms and the degree of heteroplasmies is not necessarily observed for all cases, though there is a tendency that patients with less wild type mtDNAs show severer clinical symptoms and earlier onset.     

A Supply of Nitrogen Causes Increase in the Level of NADH-Dependent Glutamate Synthase Protein and in the Activity of the Enzyme in Roots of Rice Seedlings

When rice seedlings, after the growth for 26 days in water alone,were transferred to nutrient medium contained 1 mM NH₄Cl, thelevel of NADH-dependent glutamate synthase (GOGAT) protein andthe activity of the enzyme increased more than 10-fold in root,but not in shoots. Both the level of the protein and the activityreached a maximum within 24 h. NH₄Cl was effective at concentrationsas low as 50 µM. A supply of either 1 mM NaNO₃ or 0.5mM NH₄NO₃ also caused such increases, but NHa₄Cl was most effective.A supply of glutamine or glutamate was less effective. The increasewas specific to NADH-GOGAT and little change was observed inthe levels of ferredoxin-GOGAT and glutamine synthetase isoproteinsin roots. These inducible increases in the levels of NADH-GOGATprotein and in its activity were greater in the root-tip regionthan at the base of the root. Both 6-methylpurine and cycloheximidecompletely inhibited the effects of NH₄Cl. Moreover, the mRNAfor NADH-GOGAT in rice roots accumulated markedly within 12h of the start of a supply of NH₄Cl. A possible role for therapid response of NADH-GOGAT to a supply of NH₄C1 is discussed. (Received May 18, 1995; Accepted July 10, 1995)