Bacterial pili, filamentous adhesive structures that extend from the cell surface, are important virulence factors and potential vaccine targets. Pili from Gram-negative bacteria have been structurally characterized. Now
Kang \u003cem\>et al.\u003c/em\>\u003c/b\> (p. \u003ca href\u003d\"http://www.sciencemag.org/cgi/content/short/318/5856/1625\" target\u003d\"_blank\" onclick\u003d\"return top.js.OpenExtLink(window,event,this)\"\>1625\u003c/a\>; \nsee the Perspective by \u003cb\>\u003ca href\u003d\"http://www.sciencemag.org/cgi/content/full/318/5856/1558\" target\u003d\"_blank\" onclick\u003d\"return top.js.OpenExtLink(window,event,this)\"\>Yeates and \nClubb\u003c/a\>\u003c/b\>) describe the structure of the major pilin subunit from a \nGram-positive human pathogen, \u003cem\>Streptococcus pyogenes\u003c/em\>. In the \ncrystal, the subunits associate in columns reminiscent of the likely \narrangement in native pili. The structure also reveals intramolecular \nisopeptide bonds that may stabilize the structure and contribute to \nprotease resistance. This could be a more general mechanism of protein \nstabilization in Gram-positive organisms, which lack the disulfide bond \nformation machinery of Gram-negative bacteria.\u003cp\>\n\u003cfont size\u003d\"-2\"\>CREDIT: KANG \u003cem\>ET \nAL.\u003c/em\>\u003c/font\>\u003c/p\>\u003c/td\>\u003c/tr\>\u003c/table\>\u003c/blockquote\>\n\u003chr\>\n\n\n\n\n\u003cp\>\n\n\n\u003chr\>\n\n\u003ch3\>Dissecting X Inactivation\u003c/h3\>\n\n\u003cp\>\n\n\n\n\n\nOne of the two X chromosomes in mammalian females is randomly inactivated \n\nearly in development to match the single active X chromosome of males. \n\nThis process is regulated through the X-inactivation center (Xic). The two\n\nXics interact in \u003cem\>trans\u003c/em\> at the beginning of X-inactivation, \n\npresumably to allow reciprocal activation/inactivation. So far, single \n\ncopies of elements from the Xic have not been able to recapitulate X \n\ninactivation, suggesting additional elements must be required. \u003cb\>Augui \n\n\u003cem\>et al.\u003c/em\>\u003c/b\> (p. \u003ca href\u003d\"http://www.sciencemag.org/cgi/content/short/318/5856/1632\" target\u003d\"_blank\" onclick\u003d\"return top.js.OpenExtLink(window,event,this)\"\>1632\u003c/a\>)\n\nfind that a region ~200 kilobases upstream of the Xic--the \n\nX-pairing-region (\u003cem\>Xpr\u003c/em\>) --is sufficient in a single copy to allow \n\na transient interaction between the two Xics at a time before the \n\nbeginning of X inactivation. This pairing is cell cycle dependent, can \n\noccur from an ectopic location, and may activate the expression of \n\n",1]
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Kang et al. (p. 1625; see the Perspective by Yeates and Clubb) describe the structure of the major pilin subunit from a Gram-positive human pathogen, Streptococcus pyogenes. In the crystal, the subunits associate in columns reminiscent of the likely arrangement in native pili. The structure also reveals intramolecular isopeptide bonds that may stabilize the structure and contribute to protease resistance. This could be a more general mechanism of protein stabilization in Gram-positive organisms, which lack the disulfide bond formation machinery of Gram-negative bacteria.