Nuclear DNA

About: Nuclear DNA is a research topic. Over the lifetime, 3933 publications have been published within this topic receiving 185830 citations.

Function of mitochondrial DNA in yeast.

Abstract: MITOCHONDRIA contain small amounts of DNA which differ in several chemical and physical properties from nuclear DNA (reviewed in ref. 1). Mitochondrial DNA (MDNA) of yeast2–6 is replicated by a mitochondrial DNA polymerase7 which is different from the nuclear enzyme. (unpublished results of U. Wintersberger and E. W.). A genetic function of MDNA is indicated because it serves as a template for a mitochondrial RNA polymerase8,9. Mitochondrial RNA (MRNA) has been isolated and characterized using highly purified yeast mitochondria. MRNA of yeast separates into three species when subjected to sucrose gradient centrifugation, one with a sedimentation coefficient of about 4S, the other two sedimenting faster. The 4S RNA accepts amino-acids in a manner similar to cytoplasmic tRNA; the other two RNA components were assumed to be derived from mitochondrial ribosomes9. The two ribosomal RNA (rRNA) components of the mitochondria differ in their sedimentation properties from 25S and 17S RNA of the cytoplasmic 80S ribosomes of yeast, and, in contrast, closely resemble the 23S and 16S RNA species of bacterial 70S ribosomes10,11. Hybridization experiments show that yeast MRNA hybridizes readily with MDNA, in sharp contrast to cytoplasmic rRNA which forms hybrids with MDNA very poorly but anneals extensively to nuclear DNA11,12.

Nucleolar disruption and cajal body disassembly are nuclear hallmarks of DNA damage-induced neurodegeneration in purkinje cells.

Abstract: The Purkinje cell (PC) degeneration (pcd) phenotype results from mutation in nna1 gene and is associated with the degeneration and death of PCs during the postnatal life. Although the pcd mutation is a model of the ataxic mouse, it shares clinical and pathological characteristics of inherited human spinocerebellar ataxias. PC degeneration in pcd mice provides a useful neuronal system to study nuclear mechanisms involved in DNA damage-dependent neurodegeneration, particularly the contribution of nucleoli and Cajal bodies (CBs). Both nuclear structures are engaged in housekeeping functions for neuronal survival, the biogenesis of ribosomes and the maturation of snRNPs and snoRNPs required for pre-mRNA and pre-rRNA processing, respectively. In this study, we use ultrastructural analysis, in situ transcription assay and molecular markers for DNA damage, nucleoli and CB components to demonstrate that PC degeneration involves the progressive accumulation of nuclear DNA damage associated with disruption of nucleoli and CBs, disassembly of polyribosomes into monoribosomes, ribophagy and shut down of nucleolar and extranucleolar transcription. Microarray analysis reveals that four genes encoding repressors of nucleolar rRNA synthesis (p53, Rb, PTEN and SNF2) are upregulated in the cerebellum of pcd mice. Collectively, these data support that nucleolar and CB alterations are hallmarks of DNA damage-induced neurodegeneration.

SV40 large T-antigen disturbs the formation of nuclear DNA-repair foci containing MRE11.

Abstract: The accumulation of DNA repair proteins at the sites of DNA damage can be visualized in mutagenized cells at the single cell level as discrete nuclear foci by immunofluorescent staining. Formation of nuclear foci in irradiated human fibroblasts, as detected by antibodies directed against the DNA repair protein MRE11, is significantly disturbed by the presence of the viral oncogene, SV40 large T-antigen. The attenuation of foci formation was found in both T-antigen immortalized cells and in cells transiently expressing T-antigen, indicating that it is not attributable to secondary mutations but to T-antigen expression itself. ATM-mediated nibrin phosphorylation was not altered, thus the disturbance of MRE11 foci formation by T-antigen is independent of this event. The decrease in MRE11 foci was particularly pronounced in T-antigen immortalized cells from the Fanconi anaemia complementation group FA-D2. FA-D2 cells produce essentially no MRE11 DNA repair foci after ionizing irradiation and have a significantly increased cellular radiosensitivity at low radiation doses. The gene mutated in FA-D2 cells, FANCD2, codes for a protein which also locates to nuclear foci and may, therefore, be involved in MRE11 foci formation, at least in T-antigen immortalized cells. This finding possibly links Fanconi anaemia proteins to the frequently reported increased sensitivity of Fanconi anaemia cells to transformation by SV40. From a practical stand point these findings are particularly relevant to the many studies on DNA repair which exploit the advantages of SV40 immortalized cell lines. The interference of T-antigen with DNA repair processes, as demonstrated here, should be borne in mind when interpreting such studies.

The Nucleolus: In Genome Maintenance and Repair.

Abstract: The nucleolus is the subnuclear membrane-less organelle where rRNA is transcribed and processed and ribosomal assembly occurs. During the last 20 years, however, the nucleolus has emerged as a multifunctional organelle, regulating processes that go well beyond its traditional role. Moreover, the unique organization of rDNA in tandem arrays and its unusually high transcription rates make it prone to unscheduled DNA recombination events and frequent RNA:DNA hybrids leading to DNA double strand breaks (DSBs). If not properly repaired, rDNA damage may contribute to premature disease onset and aging. Deregulation of ribosomal synthesis at any level from transcription and processing to ribosomal subunit assembly elicits a stress response and is also associated with disease onset. Here, we discuss how genome integrity is maintained within nucleoli and how such structures are functionally linked to nuclear DNA damage response and repair giving an emphasis on the newly emerging roles of the nucleolus in mammalian physiology and disease.