Suppression of tif-mediated induction of SOS functions in Escherichia coli by an altered dnaB protein

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Abstract
The tif-1 mutation in the E. coli recA gene causes induction of the various SOS functions at high temperature, including massive synthesis of the recA protein, lethal filamentation, elevated mutagenesis and, in .lambda. lysogens, induction of prophage. The DNA initiation mutation dnaB252 suppresses all these manifestations of tif expression. Induction of .lambda. by UV irradiation is not affected by the dnaB252 mutation. No similar suppression of tif is observed with other dnaB mutations affecting DNA elongation or with other DNA initiation mutations at the dnaA and dnaC loci. Since alteration of the dnaB protein specifically suppresses tif-mediated SOS induction, a role of the replication apparatus is implied in this process, as was suggested for UV induction. The induction of .lambda. proceeds via repressor cleavage, presumably promoted by an activated (protease) form of the recA protein. Since .lambda. induction is normal after UV irradiation of the tif-1 dnaB252 (.lambda.) strain, tif-mediated induction in this strain may be blocked in a tif-specific step leading to activation of the recA (tif) protein. The recA (tif) mutant protein may be directly involved in the replication complex in processes leading to this activation.