RESUMO
A 16-kilobase region surrounding the transcription initiation site for ribosomal DNA and including the entire ribosomal DNA transcription unit has been characterized in man and compared in higher primates. Restriction analysis of ribosomal DNA from the pygmy chimpanzee (Pan paniscus), the common chimpanzee (Pan troglodytes), the gorilla (Gorilla gorilla), the orangutan (Pongo pygmaeus), the gibbon (Hylobates lar), and the rhesus monkey (Macaca mulatta) allows a primate phylogeny to be constructed based on ribosomal DNA structure. Individual variation and methylation are demonstrated in the ribosomal DNA repeats of all primates examined. Restriction analysis with HincII endonuclease suggests cleavage at sites containing methylated CpG and adds the SalI/HincII pair to those enzymes useful for studying DNA modification.
Assuntos
DNA Ribossômico/genética , Primatas/genética , Animais , Evolução Biológica , Variação Genética , Humanos , Transcrição GênicaRESUMO
A group of human ribosomal DNA (rDNA) recombinants that include the probable site for initiation of transcription have been examined for sequence polymorphism. A detailed restriction map of one rDNA insert was constructed using plasmid subclones and end-labeled segments. Comparison of 16 similar rDNA inserts by restriction and heteroduplex analysis demonstrated striking conservation of the external transcribed spacer and 18S gene regions, but defined a region where restriction sites for the enzymes Sma I, Hpa II, and Hha I become frequent or variable. This region extends for about 400--800 base pairs (bp) at the left end of the rDNA insert and is postulated to contain nontranscribed spacer sequences. The use of cloned rDNA segments as probes for the restriction analysis of genomic rDNA has demonstrated certain fixed sites in the nontranscribed spacer that do not vary significantly among different individuals or tumor cell lines. In contrast, restriction with the enzyme Sal I reveals several variable fragments, one of which has been found only in a retinoblastoma cell line.
Assuntos
DNA Recombinante/análise , DNA Ribossômico , Desoxirribonucleases de Sítio Específico do Tipo I , Transcrição Gênica , Composição de Bases , Sequência de Bases , Enzimas de Restrição do DNA , Regulação da Expressão Gênica , Variação Genética , Humanos , Polimorfismo GenéticoRESUMO
Restriction endonuclease analysis of HeLa cells and cells in which origins have been questioned provides evidence in favor of a HeLa cell origin for the questioned cells. Digestion of cellular human DNA reveals a variable ribosomal DNA (rDNA) fragment that is present in up to four discrete sizes. Cell lines of known and suspected HeLa origin contain only two size variants. This pattern of variability serves to distinguish HeLa-derived cells from others. Despite repeated passage and divergence of the HeLa phenotype and karyotype, the restriction pattern is remarkably constant.
