FIG. 1.

(A) Repeating subunit of the acidic EPS from NGR234 (9). Additional acetyl groups are present at unidentified positions. (B) Genetic map of the exo cluster of pNGR234b (38). The exs genes and neighboring exoB gene are not shown. BamHI fragments were cloned into pBluescript II KS(+), yielding pExo8867, pExo9987, and pExo1888. Seven exo genes were mutated by insertion of Ω interposons at the restriction sites indicated. The pexoK plasmid is a pLAFR6 derivative carrying the 2.9-kb BamHI-ApaI fragment indicated. Computer analyses predicted that exoLAMON and exoFQZ form operons. Biochemical characteristics and symbiotic phenotypes of NGRΩexoK, NGRΩexoP, and NGRΩexoZ can be attributed to site-specific mutations.