Escape of DNA from mitochondria to the nucleus in Saccharomyces cerevisiae

The migration of genetic information from ancestral prokaryotic endosymbionts into eukaryotic nuclei is thought to have had an important role in the evolution of mitochondria and chloroplasts. Here we describe an assay for the detection of movement of DNA between mitochondria and the nucleus in yeast. Because recombinant plasmid DNA replicates after transformation into mitochondria of yeast strains lacking endogenous mitochondrial DNA we were able to propagate the nuclear genetic marker URA3 in mitochondria. As expected, the wild-type URA3 gene in mitochondria failed to complement the uracil auxotrophy (Ura-) caused by a nuclear ura3 mutation. But selection of Ura+ prototrophs from a Ura- strain carrying URA3 on a plasmid in its mitochondria enabled us to detect plasmid movement to the nucleus. Conversely, as the plasmid used also contained the mitochondrial gene COX2 required for respiratory growth, we were able to set up corresponding selections to detect migration of DNA from the nucleus to the mitochondria. Our results show that, in yeast, DNA escapes from mitochondria and appears in the nucleus at a surprisingly high frequency (approximately 2 x 10(-5) per cell per generation). But the rate at which DNA makes the journey in the opposite direction--nucleus to mitochondria--is apparently at least 100,000 times less.     

Processing of a minimal antigenic peptide alters its interaction with MHC molecules

Before their recognition by T lymphocytes, protein antigens generally require processing by antigen-presenting cells. In a poorly understood series of events, the protein antigen is internalized, transformed and re-expressed on the surface of the antigen-presenting cell in association with gene products of the major histocompatibility complex (MHC). Small peptides derived from the native protein can be recognized in the absence of antigen processing, suggesting that processing involves proteolytic degradation. These peptides are thought to mimic the naturally produced peptide fragment. We describe here a synthetic peptide antigen of this type which does not require processing but which is nevertheless further processed by splenic antigen-presenting cells. Interestingly, this processing event specifically alters the interaction of the peptide with the class II MHC (Ia) molecule, markedly affecting both its potency as an antigen in vitro and its immunogenicity in vivo (IR gene control).     

Age differences in the cellular response to cerebral lesions in the dog and mouse

Zusammenfassung Die zelluläre Reaktion an traumatischen, mechanisch gesetzten Läsionen in der Gehirnrinde wurde an neugeborenen und erwachsenen Hunden sowie an Mäusen untersucht. Die Heilung der Läsionen in Neugeborenen war so, dass das Gehirngewebe makroskopisch normal aussah; histologisch waren die durchtrennten Elemente durch die Heilungsprozesse unter minimaler glialer Reaktion wieder gut reorganisiert.     

Glucose-6-phosphatase activity in experimental tuberculosis and following isoniazid treatment

Zusammenfassung Bei den tuberkulösen Meerschweinchen wurde in der Niere eine erhöhte Aktivität der Glukose-6-Phosphatase beobachtet. Isoniazid hat die erhöhte Aktivität des Enzyms nicht erniedrigt, wenn es tuberkulösen Tieren vom 8. bis zum 38. Tage nach der Infektion oral verabreicht wurde. Es wird angenommen, dass die erhöhte Aktivität Ausdruck der Adaptionsfähigkeit von Glukose-6-Phosphatase ist.

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Galesburg State Research Hospital, Galesburg, Illinois, USA.