Summary: A gene encoding a positive activator of the expression of extracellular polysaccharide (EPS) synthesis in the phytopathogen has been isolated from a genomic library in . The presence of the cloned gene in stimulated transcription of the genes encoding colanic acid biosynthesis and could complement mutations. Introduction of the gene on a multicopy plasmid into caused a threefold increase in EPS expression. The nucleotide sequence of the gene (designated ) was determined. This revealed a single open reading frame encoding an RcsA protein of 23·7 kDa. This was confirmed by minicell analysis in . The predicted amino acid sequence of this RcsA protein showed a high degree of homology to the RcsA protein of , demonstrating the existence of a family of related RcsA activator proteins capable of stimulating EPS expression. The protein had no significant homology to known DNA-binding activator proteins, indicating, for the first time, that the RcsA family of activator proteins may stimulate expression of EPS synthesis indirectly by acting on other regulatory proteins.


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