Mais de rien Juju, de rien...
Parlez moi de ça: un cancre faisant acte d'autorité !
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Annu Rev Genomics Hum Genet 2000;1:99-116
How many genes can make a cell: the minimal-gene-set concept.
Koonin EV.
National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, Maryland 20894, USA. koonin@ncbi.nlm.nih.gov
Several theoretical and experimental studies have endeavored to derive the minimal set of genes that are necessary and sufficient to sustain a functioning cell under ideal conditions, that is, in the presence of unlimited amounts of all essential nutrients and in the absence of any adverse factors, including competition. A COMPARISON OF THE FIRST TWO COMPLETED BACTERIAL GENOMES, THOSE OF THE PARASITES HAEMOPHILUS INFLUENZAE AND MYCOPLASMA GENITALIUM, PRODUCED A VERSION OF THE MINIMAL GENE SET CONSISTING OF APPROXIMATELY 250 GENES. VERY SIMILAR ESTIMATES WERE OBTAINED BY ANALYZING VIABLE GENE KNOCKOUTS IN BACILLUS SUBTILIS, M. GENITALIUM, AND MYCOPLASMA PNEUMONIAE. With the accumulation and comparison of multiple complete genome sequences, it became clear that only approximately 80 genes of the 250 in the original minimal gene set are represented by orthologs in all life forms. For approximately 15% of the genes from the minimal gene set, viable knockouts were obtained in M. genitalium; unexpectedly, these included even some of the universal genes. Thus, some of the genes that were included in the first version of the minimal gene set, based on a limited genome comparison, could be, in fact, dispensable. The majority of these genes, however, are likely to encode essential functions but, in the course of evolution, are subject to nonorthologous gene displacement, that is, recruitment of unrelated or distantly related proteins for the same function. Further theoretical and experimental studies within the framework of the minimal-gene-set concept and the ultimate construction of a minimal genome are expected to advance our understanding of the basic principles of cell functioning by systematically detecting nonorthologous gene displacement and deciphering the roles of essential but functionally uncharacterized genes.
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Wien Klin Wochenschr 1997 Aug 8;109(14-15):551-6
Comparative genomics of mycoplasmas.
Razin S.
Department of Membrane and Ultrastructure Research, Hebrew University-Hadassah Medical School, Jerusalem, Israel.
The mycoplasmas are the smallest and simplest self-replicating organisms. The goal of defining in molecular terms the entire machinery of a living cell by using mycoplasmas as models was put forward by Harold Morowitz in 1984. The recent complete sequencing of the genomes of the human pathogens Mycoplasma genitalium and Mycoplasma pneumoniae brings us much closer to achieving this goal. THE M. GENITALIUM GENOME CONTAINS ONLY 479 PREDICTED PROTEIN CODING SEQUENCES (GENES) and that of M. pneumoniae 677, as compared with 1703 in Haemophilus influenzae and about 4000 in E. coli. Thus, M. genitalium is apparently the simplest organism capable of independent life with a minimal set of genes. The drastic economization in genetic information must have been associated
with the parasitic mode of life of the mycoplasmas. During their reductive evolution from Gram-positive bacteria the mycoplasmas have lost the cell wall and many biosynthetic systems involved in synthesis of macromolecule building blocks provided by their host. Thus, the M. genitalium and M. pneumoniae genomes do not carry any gene involved in amino acid biosynthesis, and very few genes for vitamin, nucleic acid precursor and fatty acid biosynthesis. The mycoplasma genomes carry a minimal set of energy metabolism genes, being content with a restricted supply of ATP needed for their parasitic mode of life. Nevertheless,these minimal organisms carry the essential genes for DNA replication, transcription and translation, but even here gene saving is expressed by a minimal number of rRNA and tRNA genes. A genomic price had been paid to maintain parasitism, so that a significant number of mycoplasmal genes is devoted to adhesins, attachment organelles and variable membrane surface antigens directed towards evasion of the host immune system.
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"Je CROIS à ça moi, la « Reductive Evolution »." [Nounouille]
Merci de transporter le débat sur la plateforme qui constitue ta spécialité: La CROYANCE
Ce que le spécialiste de la "thermodimanie" CROIT ou ne CROIT PAS n'a que peu d'importance quand il commente (sous inspiration divine) l'interprétation de la séquence génomique de Mycoplasma pneumoniae.
Ca te va comme des guêtres à un poulet.
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