Nuclear DNA

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

Preferential alkylation of mitochondrial deoxyribonucleic acid by N-methyl-N-nitrosourea

Abstract: The reaction of the carcinogen N-methyl-N-nitrosourea with mitochondrial DNA from various rat tissues was examined in vivo and in vitro. After incubation of isolated mitochondria or cell nuclei with N[14C]-methyl-N-nitrosourea in vitro and subsequent isolation and purification of the DNA the specific radioactivity of the mitochondrial DNA was 3–7 times that of the nuclear DNA. The incorporation of 14C into embryonic mitochondrial DNA in vitro was about twice that into the liver mitochondrial DNA. Identical incorporation rates, however, were found for the reaction of isolated mitochondrial DNA or nuclear DNA respectively with N[14C]-methyl-N-nitrosourea. After intraperitoneal injection of 43.3–58.5mg of N[14C]-methyl-N-nitrosourea/kg body wt. to adult rats the labelling of the mitochondrial DNA was on average 5 times that of the nuclear DNA. A smaller specific labelling was observed for the ribosomal RNA, transfer RNA, and mitochondrial RNA as well as for the mitochondrial protein as compared with the mitochondrial DNA. After hydrolysis of the alkylated nucleic acids with hydrochloric acid, fractionation was carried out on Dowex 50 cation-exchange columns. In most experiments 70–80% of the input 14C radioactivity was eluted in the 7-methylguanine fraction. The preferential alkylation of the mitochondrial DNA by N-methyl-N-nitrosourea in situ is discussed in connexion with the cytoplasmic-mutation hypothesis of carcinogenesis.

Intergeneric somatic hybridization and its application to crop genetic improvement

Abstract: Related or distant species of cultivated cs are a large pool of many desirable genes. Gene transfer from these species through conventional breeding is difficult owing to post- and pre-zygotic sexual incompatibilities. Somatic hybridization via protoplast fusion is a possible alternative for gene transfer from these species to cultivated crops. Since the early days of somatic hybridization many intergeneric somatic hybrids have been developed through symmetric fusion, asymmetric fusion and microfusion. Somatic hybrids are mainly selected by using markers such as specific media or fusion parents with special features, biochemical mutants, antibiotic resistance and complementation strategy. The hybridity of the regenerants is determined based on morphological, cytological and molecular analysis. The inheritance patterns of nuclear and cytoplasmic genomes in the somatic hybrids are diverse. Nuclear DNA from both fusion parents co-exists congruously in some hybrids with translocation and rearrangement of chromosomes, but spontaneous elimination of chromosomes from either or both fusion parents has been observed very often. In asymmetric fusion, chromosome elimination is an important issue that is a complicated process influenced by many factors, such as irradiation dose, phylogenetic relatedness, ploidy level of fusion parent and regenerants. As for chloroplast genome, uniparental segregation is mainly detected, though co-existence is also reported in some cases. The mitochondrial genome, in contrast to chloroplast, undergoes recombination and very frequent rearrangements. Somatic cell fusion has potential applications for crop genetic improvement by overcoming sexual incompatibility or reproductive barriers, and by realizing novel combinations of nuclear and/or cytoplasmic genomes.

Mitochondrial DNA-like sequences in the nucleus (NUMTs): insights into our African origins and the mechanism of foreign DNA integration.

Abstract: Nuclear mitochondrial DNA sequences (NUMTs) are common in eukaryotes. However, the mechanism by which they integrate into the nuclear genome remains a riddle. We analyzed 247 NUMTs in the human nuclear DNA (nDNA), along with their flanking regions. This analysis revealed that some NUMTs have accumulated many changes, and thus have resided in the nucleus a long time, while others are >94% similar to the reference human mitochondrial DNA (mtDNA), and thus must be recent. Among the latter, two NUMTs, encompassing the COI gene, carry a set of transitions characteristic of the extant African-specific L macrohaplogroup mtDNAs and are more homologous to human mtDNA than to chimp. Screening for one of these NUMTs revealed its presence in all human samples tested, confirming that the African macrohaplogroup L mtDNAs were present in the earliest modern humans and thus were the first human mtDNAs. An analysis of flanking sequences of the NUMTs revealed that 59% were within 150 bp of repetitive elements, with 26% being within 15 bp of and 33% being within 15–150 bp of repetitive elements. Only 14% were integrated into a repetitive element. This association of NUMTs with repetitive elements is highly nonrandom (p<0.001). These data suggest that the vicinity of transposable elements influences the ongoing integration of mtDNA sequences and their subsequent duplication within the nDNA. Finally, NUMTs appear to preferentially integrate into DNA with different GC content than the surrounding chromosomal band. Our results suggest that chromosomal structure might influence integration of NUMTs. Hum Mutat 23:125–133, 2004. © 2003 Wiley-Liss, Inc.