FILAMENTOUS PHAGE INFECTION - REQUIRED INTERACTIONS WITH THE TOLA PROTEIN

Infection of Escherichia coli by the filamentous phage fl is initiated by binding of the phage to the tip of the F conjugative pilus via the gene III protein, Subsequent translocation of phage DNA requires the chromosomally encoded TolQ, TolR, and TolA proteins, after the pilus p resumably has withdrawn, bringing the phage to the bacterial surface. Of these three proteins, TolA is proposed to span the periplasm, since it contains a long helical domain (domain II), which connects a cytop lasmic membrane anchor domain (domain I) to the carboxyl-terminal doma in (domain III), By using a transducing phage, the requirement for Tol A in an F+ strain was found to be absolute. The role of TolA domains I I and III in the infective process was examined by analyzing the abili ty of various deletion mutants of tolA to facilitate infection, The C- terminal domain III was shown to be essential, whereas the polyglycine region separating domains I and II could be deleted with no effect, D eletion of helical domain II. reduced the efficiency of infection, whi ch could be restored to normal by retaining the C-terminal half of dom ain II, Soluble domain III, expressed in the periplasm but not in the cytoplasm or in the medium, interfered with infection of a tolA(+) str ain, The essential interaction of TolA domain III with phage via gene III protein appears to require interaction with a third component, eit her the pilus tip or a periplasmic entity.