RecA: Diferenzas entre revisións
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Liña 55:
A [[transformación (xenética)|transformación]] bacteriana natural implica a transferencia de [[ADN]] desde unha bacteria a outra (normalmente da mesma especie) e a integración do ADN doante no [[cromosoma]] receptor por [[recombinación homóloga]], un proceso mediado pola proteína RecA (ver [[Transformación (xenética)]]). A transformación, na cal RecA xoga un papel central, depende da expresión de numerosos produtos xénicos adicionais (por exemplo, uns 40 produtos xénicos en ''[[Bacillus subtilis]]''), que interaccionan especificamente para levar a cabo este proceso indicando que é unha [[adaptación biolóxica|adaptación]] que [[evolución|evolucionou]] para a transferencia de ADN. En ''B. subtilis'' a lonxitude do ADN transferido pode ser do tamaño dun terzo ata un cromosoma completo.<ref name="pmid11388459">{{cite journal |vauthors=Akamatsu T, Taguchi H |title=Incorporation of the whole chromosomal DNA in protoplast lysates into competent cells of Bacillus subtilis |journal=Biosci. Biotechnol. Biochem. |volume=65 |issue=4 |pages=823–9 |date=April 2001 |pmid=11388459 |doi= 10.1271/bbb.65.823|url=}}</ref><ref name="pmid16716928">{{cite journal |vauthors=Saito Y, Taguchi H, Akamatsu T |title=Fate of transforming bacterial genome following incorporation into competent cells of Bacillus subtilis: a continuous length of incorporated DNA |journal=J. Biosci. Bioeng. |volume=101 |issue=3 |pages=257–62 |date=March 2006 |pmid=16716928 |doi=10.1263/jbb.101.257 |url=}}</ref> Para que unha bacteria se una, capte e recombina ADN exóxeno no seu cromosoma, debe primeiro entrar nun estado fisiolóxico especial chamado “competencia” ([[competencia natural]]). A transformación é algo común no mundo procariota, e ata agora coñécense 67 especies que son competentes para a transformación.<ref name="pmid17997281">{{cite journal |vauthors=Johnsborg O, Eldholm V, Håvarstein LS |title=Natural genetic transformation: prevalence, mechanisms and function |journal=Res. Microbiol. |volume=158 |issue=10 |pages=767–78 |date=December 2007 |pmid=17997281 |doi=10.1016/j.resmic.2007.09.004 |url=}}</ref>
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One of the most well studied transformation systems is that of [[Bacillus subtilis|''B. subtilis'']]. In this bacterium, the RecA protein interacts with the incoming single-stranded DNA (ssDNA) to form striking filamentous structures.<ref name="pmid16009134">{{cite journal |vauthors=Kidane D, Graumann PL |title=Intracellular protein and DNA dynamics in competent Bacillus subtilis cells |journal=Cell |volume=122 |issue=1 |pages=73–84 |date=July 2005 |pmid=16009134 |doi=10.1016/j.cell.2005.04.036 |url=http://linkinghub.elsevier.com/retrieve/pii/S0092-8674(05)00551-9}}</ref> These RecA/ssDNA filaments emanate from the cell pole containing the competence machinery and extend into the cytosol. The RecA/ssDNA filamentous threads are considered to be dynamic nucleofilaments that scan the resident chromosome for regions of homology. This process brings the incoming DNA to the corresponding site in the ''B. subtilis'' chromosome where informational exchange occurs.▼
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Michod et al.<ref name="pmid18295550">{{cite journal |vauthors=Michod RE, Bernstein H, Nedelcu AM |title=Adaptive value of sex in microbial pathogens |journal=Infect. Genet. Evol. |volume=8 |issue=3 |pages=267–85 |date=May 2008 |pmid=18295550 |doi=10.1016/j.meegid.2008.01.002 |url=http://linkinghub.elsevier.com/retrieve/pii/S1567-1348(08)00004-X}}</ref> have reviewed evidence that RecA-mediated transformation is an adaptation for homologous recombinational repair of DNA damage in ''B. subtilis'', as well as in several other bacterial species (i.e. ''[[Neisseria gonorrhoeae]], [[Hemophilus influenzae]], [[Streptococcus pneumoniae]], [[Streptococcus mutans]]'' and ''[[Helicobacter pylori]]''). In the case of the pathogenic species that infect humans, it was proposed that RecA-mediated repair of DNA damages may be of substantial benefit when these bacteria are challenged by the oxidative defenses of their host.
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