RESUMO
One of the rewards of having a Drosophila melanogaster whole-genome sequence will be the potential to understand the molecular bases for structural features of chromosomes that have been a long-standing puzzle. Analysis of 2.6 megabases of sequence from the tip of the X chromosome of Drosophila identifies 273 genes. Cloned DNAs from the characteristic bulbous structure at the tip of the X chromosome in the region of the broad complex display an unusual pattern of in situ hybridization. Sequence analysis revealed that this region comprises 154 kilobases of DNA flanked by 1.2-kilobases of inverted repeats, each composed of a 350-base pair satellite related element. Thus, some aspects of chromosome structure appear to be revealed directly within the DNA sequence itself.
Assuntos
Drosophila melanogaster/genética , Cromossomo X/genética , Animais , Bandeamento Cromossômico , Biologia Computacional , Cosmídeos , Elementos de DNA Transponíveis , DNA Satélite , Genes de Insetos , Hibridização In Situ , Sequências Repetitivas de Ácido Nucleico , Análise de Sequência de DNA , Cromossomo X/ultraestruturaRESUMO
The scarcity of usable nitrogen frequently limits plant growth. A tight metabolic association with rhizobial bacteria allows legumes to obtain nitrogen compounds by bacterial reduction of dinitrogen (N2) to ammonium (NH4+). We present here the annotated DNA sequence of the alpha-proteobacterium Sinorhizobium meliloti, the symbiont of alfalfa. The tripartite 6.7-megabase (Mb) genome comprises a 3.65-Mb chromosome, and 1.35-Mb pSymA and 1.68-Mb pSymB megaplasmids. Genome sequence analysis indicates that all three elements contribute, in varying degrees, to symbiosis and reveals how this genome may have emerged during evolution. The genome sequence will be useful in understanding the dynamics of interkingdom associations and of life in soil environments.
Assuntos
Genoma Bacteriano , Análise de Sequência de DNA , Sinorhizobium meliloti/genética , Simbiose/genética , Aderência Bacteriana , Proteínas de Bactérias/genética , Proteínas de Transporte/genética , Cromossomos Bacterianos/genética , Biologia Computacional , Elementos de DNA Transponíveis , Metabolismo Energético/genética , Evolução Molecular , Duplicação Gênica , Genes Bacterianos , Genes Essenciais , Genes Reguladores , Medicago sativa/microbiologia , Nitrogênio/metabolismo , Fixação de Nitrogênio/genética , Plasmídeos , Polissacarídeos Bacterianos/genética , Replicon , Rhizobiaceae/genética , Sinorhizobium meliloti/fisiologiaRESUMO
Sinorhizobium meliloti is an alpha-proteobacterium that forms agronomically important N(2)-fixing root nodules in legumes. We report here the complete sequence of the largest constituent of its genome, a 62.7% GC-rich 3,654,135-bp circular chromosome. Annotation allowed assignment of a function to 59% of the 3,341 predicted protein-coding ORFs, the rest exhibiting partial, weak, or no similarity with any known sequence. Unexpectedly, the level of reiteration within this replicon is low, with only two genes duplicated with more than 90% nucleotide sequence identity, transposon elements accounting for 2.2% of the sequence, and a few hundred short repeated palindromic motifs (RIME1, RIME2, and C) widespread over the chromosome. Three regions with a significantly lower GC content are most likely of external origin. Detailed annotation revealed that this replicon contains all housekeeping genes except two essential genes that are located on pSymB. Amino acid/peptide transport and degradation and sugar metabolism appear as two major features of the S. meliloti chromosome. The presence in this replicon of a large number of nucleotide cyclases with a peculiar structure, as well as of genes homologous to virulence determinants of animal and plant pathogens, opens perspectives in the study of this bacterium both as a free-living soil microorganism and as a plant symbiont.
Assuntos
Cromossomos Bacterianos/genética , Sinorhizobium meliloti/genética , Proteínas de Bactérias/genética , Proteínas de Transporte/genética , Divisão Celular/genética , Movimento Celular/genética , Cromossomos Artificiais Bacterianos/genética , Reparo do DNA/genética , Replicação do DNA/genética , DNA Bacteriano/genética , DNA Circular/genética , Metabolismo Energético/genética , Fabaceae/microbiologia , Duplicação Gênica , Genes Bacterianos , Dados de Sequência Molecular , Plantas Medicinais , Replicon/genética , Análise de Sequência de DNA , Transdução de Sinais/genética , Simbiose , Transcrição Gênica/genética , Virulência/genéticaRESUMO
We present the sequence of a contiguous 2.63 Mb of DNA extending from the tip of the X chromosome of Drosophila melanogaster. Within this sequence, we predict 277 protein coding genes, of which 94 had been sequenced already in the course of studying the biology of their gene products, and examples of 12 different transposable elements. We show that an interval between bands 3A2 and 3C2, believed in the 1970s to show a correlation between the number of bands on the polytene chromosomes and the 20 genes identified by conventional genetics, is predicted to contain 45 genes from its DNA sequence. We have determined the insertion sites of P-elements from 111 mutant lines, about half of which are in a position likely to affect the expression of novel predicted genes, thus representing a resource for subsequent functional genomic analysis. We compare the European Drosophila Genome Project sequence with the corresponding part of the independently assembled and annotated Joint Sequence determined through "shotgun" sequencing. Discounting differences in the distribution of known transposable elements between the strains sequenced in the two projects, we detected three major sequence differences, two of which are probably explained by errors in assembly; the origin of the third major difference is unclear. In addition there are eight sequence gaps within the Joint Sequence. At least six of these eight gaps are likely to be sites of transposable elements; the other two are complex. Of the 275 genes in common to both projects, 60% are identical within 1% of their predicted amino-acid sequence and 31% show minor differences such as in choice of translation initiation or termination codons; the remaining 9% show major differences in interpretation.