J. Bacteriol., 02 1996, 1232-1236, Vol 178, No. 4
Copyright © 1996, American Society for Microbiology

Random and directed mutagenesis to elucidate the functional importance of helix II and F-989 in the C-terminal secretion signal of Escherichia coli hemolysin

C Chervaux and IB Holland
Institut de Genetique et Microbiologie, Universite Paris Sud.

The HlyA secretion signal sequence of approximately 46 residues is predicted to contain helix I and an amphipathic helix II separated by a short loop including the conserved Phe residue, F-989. All nine substitutions of Phe-989 drastically reduce secretion of HlyA. Directed mutagenesis identified a functional hot spot, EISK, in helix II. However, genetic analysis did not provide strong support for a functional helix II; rather, the results emphasized that individual residues, for example, E-978 and F-989, are essential irrespective of a specific secondary structure.

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