FORMATION OF MITOCHONDRIA IN NEUROSPORA CRASSA

Abstract

Cells of a choline-requiring mutant of Neurospora crassa, labeled with radioactive choline, were transferred to unlabeled medium. At various times during their subsequent logarithmic growth, a highly purified mitochondrial fraction was prepared by sucrose density gradient centrifugation, and the distribution of label among individual mitochondria was determined by quantitative autoradiography. Preliminary experiments indicated that, under the conditions of this "washout" experiment, choline served as a stable mitochondrial label. Radioautographic analysis showed that, in fully labeled mycelia and for three mass doubling cycles in the unlabeled medium, radioactivity was randomly distributed among all mitochondria; i.e., the distribution of autographic grains among individual mitochondria followed a Poisson distribution. In experiments in which pulse labeling for l0 minutes was used, the label was randomly distributed among all mitochondria. The data suggest that the mitochondrial mass is increased by a continuous process of addition of new lecithin units to the already existing mitochondrial framework.

Mitochondrial protein import: Specific recognition and membrane translocation of preproteins

“…Mitochondria are not synthesized de novo; they arise by growth and division of pre-existing organelles (Luck, 1963(Luck, , 1965. Mitochondria contain DNA (Schatz, Haslbrunner & Tuppy, 1964) and a complete system to carry out DNA replication, transcription, and protein synthesis (McLean et al, 1958;Tzagoloff, 1982); however, only a small number of proteins are encoded by mitochondrial DNA, namely a few subunits of the respiratory chain and the ATP synthase, and depending on the organism, one or a few proteins required for the expression of mitochondrial genes.…”

A PARACRYSTALLINE INCLUSION IN NEUROSPORA CRASSA

“…Cultures were inoculated with 7 X 105 conidia per milliliter . Hyphae were grown either in 100-150-ml samples in 1 liter Florence flasks aerated by shaking as described by Luck (1963) or as 3-liter cultures in 4-liter carboys under forced aeration at 25°C (Rifkin, Wood, and Luck, 1967) .…”

“…All conidia were produced and handled as described by Luck (1963) . Cultures were inoculated with 7 X 105 conidia per milliliter .…”

“…Mitochondria were isolated by differential and isopycnic centrifugation according to Luck (1963) . Soluble proteins were here defined as those Neurospora proteins soluble in phosphate buffer .…”

The Preparation and Biochemical Properties of Mitochondria from Neurospora crassa

“…A.) by the procedure of Luck (1963) following Britten & Roberts (1960). The same apparatus was used to collect fractions from the gradient.…”