Assuntos
DNA/análise , Sefarose , Animais , Digoxigenina , Drosophila/genética , Técnicas Genéticas , Hibridização de Ácido NucleicoRESUMO
1. Expression plasmids containing non-overlapping tandemly repeated ribosome binding sites (RBS) were constructed in order to stabilize mRNA and enhance translation. 2. Two synthetic genes (human calcitonin tetramer gene and a fusion gene human gamma-interferon-human calcitonin) were cloned in these vectors and the effect of multiplicity of Shine-Dalgarno (S/D) sequence on heterologous gene expression was studied. 3. It was found that duplication and triplication of RBS had no effect on the stability of mRNA but led to a strong decrease in the level of recombinant protein and mRNA in the cell. 4. Plasmids bearing four times repeated S/D sequences gave longer-lived mRNAs and maintained a level of protein and mRNA very close to the values obtained with a single S/D containing plasmids.
Assuntos
Calcitonina/genética , Expressão Gênica , Vetores Genéticos/genética , Plasmídeos/genética , Sequências Reguladoras de Ácido Nucleico , Sequências Repetitivas de Ácido Nucleico , Ribossomos/metabolismo , Sequência de Bases , Sítios de Ligação/genética , Calcitonina/biossíntese , Escherichia coli/genética , Humanos , Dados de Sequência Molecular , Conformação de Ácido Nucleico , Biossíntese de Proteínas , RNA Bacteriano/genética , RNA Mensageiro/genética , Radioimunoensaio , Transcrição GênicaRESUMO
Nucleotide sequences of E. coli tRNAs and RNA I or RNA II (controlling replication of ColE1 plasmids) were compared using the computer. The homology between some of these molecules is over 60%. The distribution of homologous nucleotides among the functional elements (stems and loops) of either RNA I or RNA II and the tRNAs molecules was studied. It was found that the homologous domains are located mainly in the loop regions of RNA I or RNA II. A consensus sequence, the nonanucleotide AGUUGGUAG, was discovered in loop II of RNA I and in the dihydrouridylic loop of tRNAs showing homology with RNA I. Based on this observation, a hypothesis was drawn for a possible role of the tRNAs in the regulation of plasmid DNA replication.
Assuntos
Sequência de Bases , Escherichia coli/genética , Plasmídeos , RNA Bacteriano , RNA de Transferência , Homologia de Sequência do Ácido Nucleico , Modelos Genéticos , Dados de Sequência MolecularRESUMO
We investigated the organization of the rat rDNA non-transcribed spacer (NTS) by determining the sequence of large NTS segments located upstream (2501 bp) and downstream (4025 bp) from the rRNA transcription unit. We identified four B2-like and two ID mobile elements. They may be grouped in three pairs with the members of each pair located in the upstream and downstream NTS. The ID sequences are identical to the consensus sequence, while the pairs of B2-like elements show 85% and 50/65% homology to the consensus B2 sequence. The proximal part of the downstream NTS contains a region of widely diverged SalI tandem repeats. A considerable part of the analyzed upstream and downstream NTS sequences is constituted by different types of simple sequences and long poly(purine) X poly(pyrimidine) tracts. These data show that the rat rDNA NTS regions flanking the rRNA transcription unit are characterized by a combination of short interspersed (B2-superfamily) and various simple sequences.
Assuntos
DNA Ribossômico/genética , RNA Ribossômico/genética , Sequências Repetitivas de Ácido Nucleico , Animais , Sequência de Bases , Ligação Genética , Ratos , Transcrição GênicaRESUMO
The primary structure of rat (Rattus norvegicus) 28 S rRNA is determined inferred from the sequence of cloned rDNA fragments. The rat 28 S rRNA contains 4802 nucleotides and has an estimated relative molecular mass (Mr, Na-salt) of 1.66 X 10(6). Several regions of high sequence homology with S. cerevisiae 25 S rRNA are present. These regions can be folded in characteristic base-paired structures homologous to those proposed for Saccharomyces and E. coli. The excess of about 1400 nucleotides in the rat 28 S rRNA (as compared to Saccharomyces 25 S rRNA) is accounted for mainly by the presence of eight distinct G+C-rich segments of different length inserted within the regions of high sequence homology. The G+C content of the four insertions, containing more than 200 nucleotides, is in the range of 78 to 85 percent. All G+C-rich segments appear to form strongly base-paired structures. The two largest G+C-rich segments (about 760 and 560 nucleotides, respectively) are located near the 5'-end and in the middle of the 28 S rRNA molecule. These two segments can be folded into long base-paired structures, corresponding to the ones observed previously by electron microscopy of partly denatured 28 S rRNA molecules.
