SummaryAutoinducer-2 (AI-2) a signal produced by a range of phylogenetically distant microorganisms, enables inter-species cell-cell communication and regulates many bacterial phenotypes. Certain bacteria can interfere with AI-2-regulated behaviours of neighbouring species by internalizing AI-2 using the Lsr transport system (encoded by the lsr operon). AI-2 imported by the Lsr is phosphorylated by the LsrK kinase and AI-2-phosphate is the inducer of the lsr operon. Here we show that in Escherichia coli the phosphoenolpyruvate phosphotransferase system (PTS) is required for Lsr activation and is essential for AI-2 internalization. Although the phosphorylation state of Enzyme I of PTS is important for this regulation, LsrK is necessary for the phosphorylation of AI-2, indicating that AI-2 is not phosphorylated by PTS. Our results suggest that AI-2 internalization is initiated by a PTS-dependent mechanism, which provides sufficient intracellular AI-2 to relieve repression of the lsr operon and, thus induce depletion of AI-2 from the extracellular environment. The fact that AI-2 internalization is not only controlled by the communitydependent accumulation of AI-2, but also depends on the phosphorylation state of PTS suggests that E. coli can integrate information on the availability of substrates with external communal information to control quorum sensing and its interference.

Sequence differences in the EBNA-2 protein mediate the superior ability of type 1 Epstein-Barr virus (EBV) to transform human B cells into lymphoblastoid cell lines compared to that of type 2 EBV. Here we show that changing a single amino acid (S442D) from serine in type 2 EBNA-2 to the aspartate found in type 1 EBNA-2 confers a type 1 growth phenotype in a lymphoblastoid cell line growth maintenance assay. This amino acid lies in the transactivation domain of EBNA-2, and the S442D change increases activity in a transactivation domain assay. The superior growth properties of type 1 EBNA-2 correlate with the greater induction of EBV LMP-1 and about 10 cell genes, including CXCR7. In chromatin immunoprecipitation assays, type 1 EBNA-2 is shown to associate more strongly with EBNA-2 binding sites near the LMP-1 and CXCR7 genes. Unbiased motif searching of the EBNA-2 binding regions of the differentially regulated cell genes identified an ETS-interferon regulatory factor composite element motif that closely corresponds to the sequences known to mediate EBNA-2 regulation of the LMP-1 promoter. It appears that the superior induction by type 1 EBNA-2 of the cell genes contributing to cell growth is due to their being regulated in a manner different from that for most EBNA-2-responsive genes and in a way similar to that for the LMP-1 gene. IMPORTANCE

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