Lytic conversion of Escherichia coli by bacteriophage T5: blocking of the FhuA receptor protein by a lipoprotein expressed early during infection

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Abstract
Summary: The nucleotide sequence of the region between the oad gene, encoding the host specificity protein, and the right‐terminal repetition of bacteriophage T5 DNA was determined. Five small open reading frames, the first of which was called IIp, were detected, which apparently formed an operon transcribed from a promoter that overlapped the oad promoter. Both promoters were confirmed by primer extension assays. Using mRNA isolated at different times after T5 infection, the IIp and oad promoters were identified as early and late promoters, respectively. The N‐terminus of the IIp gene product possess a signal sequence and a processing site characteristic of lipoproteins. After subcloning and expression of IIp, its product Lip was identified as a 7.8 kDa polypeptide. Acylation of Lip was confirmed by addition of globomycin, which resulted in the accumulation of the unprocessed precursor form. FhuA4 cells synthesizing Lip were resistant to phage T5. Resistance was caused by inhibition of adsorption of T5 to its FhuA receptor protein. Resistance could be overcome by derepression of fhuA transcription, suggesting a blocking of FhuA by direct interaction with Lip. Since Lip‐mediated T5 resistance has several aspects in common with the phenomenon of lysogenic conversion, we suggest that it should be called lytic conversion.