Glucosylation of Lipopolysaccharide in Salmonella: Mutants Negative for O Antigen Factor 1221

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RESUMO

In salmonella O group B, the O antigen factor 122 is created by glucosylation at C4 of the galactose units of the O side chains; phage-determined glucosylation at C6 of these galactose units yields factor 1. 122-negative mutants were isolated from 122+ (stable) parents (genetically oafR+st). All 20 mutants studied were stable in respect of their 122 character. In eight of them, lysogenization by phage P22 resulted in the appearance of the 122 factor—these were interpreted to be defective in the enzyme(s) needed to synthesize the glucose-lipid intermediate that participates in both 122- and 1-specific glucosylation; the corresponding cistron was termed oafE. This “complementation” assay also demonstrated that the P22 genome can determine the synthesis of this glucose-lipid intermediate. The 122 character in the oafE− mutants became variable after P22 lysogenization, corresponding to factor 1 variation normally determined by this phage. In the remaining 12 mutants, P22 caused the appearance of a variable factor 1, but not of 122. The lesion in all the 122 mutants was mapped close to the gene purE at min 19 of the Salmonella map. This is the same area where the locus oafR that controls the variation (stable or variable, + or −) of 122 had been previously mapped. The results suggest the presence of a 122 glucosylation operon in this region.

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