http://hdl.handle.net/2027.42/78359 2013-05-19T08:04:18Z http://hdl.handle.net/2027.42/92200 Cycling of Etk and Etp Phosphorylation States Is Involved in Formation of Group 4 Capsule by Escherichia coli Nadler, Chen; Koby, Simi; Peleg, Adi; Johnson, Austin C.; Suddala, Krishna C.; Sathiyamoorthy, Karthik; Smith, Bennett E.; Saper, Mark A.; Rosenshine, Ilan Capsules frequently play a key role in bacterial interactions with their environment. Escherichia coli capsules were categorized as groups 1 through 4, each produced by a distinct mechanism. Etk and Etp are members of protein families required for the production of group 1 and group 4 capsules. These members function as a protein tyrosine kinase and protein tyrosine phosphatase, respectively. We show that Etp dephosphorylates Etk in vivo, and mutations rendering Etk or Etp catalytically inactive result in loss of group 4 capsule production, supporting the notion that cyclic phosphorylation and dephosphorylation of Etk is required for capsule formation. Notably, Etp also becomes tyrosine phosphorylated in vivo and catalyzes rapid auto-dephosphorylation. Further analysis identified Tyr121 as the phosphorylated residue of Etp. Etp containing Phe, Glu or Ala in place of Tyr121 retained phosphatase activity and catalyzed dephosphorylation of Etp and Etk. Although EtpY121E and EtpY121A still supported capsule formation, EtpY121F failed to do so. These results suggest that cycles of phosphorylation and dephosphorylation of Etp, as well as Etk, are involved in the formation of group 4 capsule, providing an additional regulatory layer to the complex control of capsule production. 2012-01-01T00:00:00Z http://hdl.handle.net/2027.42/92199 Identification of an Escherichia coli operon required for formation of the O-antigen capsule Peleg, Adi; Shifrin, Yulia; Ilan, Ophir; Nadler-Yona, Chen; Nov, Shani; Koby, Simi; Baruch, Kobi; Altuvia, Shoshy; Elgrably-Weiss, Maya; Abe, Cecilia M.; Knutton, Stuart; Saper, Mark A.; Rosenshine, Ilan Escherichia coli produces polysaccharide capsules that, based on their mechanisms of synthesis and assembly, have been classified into four groups. The group 4 capsule (G4C) polysaccharide is frequently identical to that of the cognate lipopolysaccharide O side chain and has, therefore, also been termed the O-antigen capsule. The genes involved in the assembly of the group 1, 2, and 3 capsules have been described, but those required for G4C assembly remained obscure. We found that enteropathogenic E. coli (EPEC) produces G4C, and we identified an operon containing seven genes, ymcD, ymcC, ymcB, ymcA, yccZ, etp, and etk, which are required for formation of the capsule. The encoded proteins appear to constitute a polysaccharide secretion system. The G4C operon is absent from the genomes of enteroaggregative E. coli and uropathogenic E. coli. E. coli K-12 contains the G4C operon but does not express it, because of the presence of IS1 at its promoter region. In contrast, EPEC, enterohemorrhagic E. coli, and Shigella species possess an intact G4C operon. 2005-11-01T00:00:00Z http://hdl.handle.net/2027.42/85745 Selection of RNA aptamers that bind HIV-1 LTR DNA; strand invaders Engelke, David R. 2010-01-01T00:00:00Z http://hdl.handle.net/2027.42/85744 Cellular dynamics of tRNAs and their genes Engelke, David R. 2010-01-01T00:00:00Z