FIG. 3.

SecB dependence of mutant alkaline phosphatases with signal peptides of different hydrophobicity and with the basic motif (K5L5) in the early mature region. (A) Alkaline phosphatase is shown diagrammatically as in Fig. 1A and 2A. The hydrophobic core region (hatched) of the signal peptide was replaced with various hydrophobic sequences while maintaining the K5L5 motif (checkered) in the early mature region. (B) Precursor processing of the mutant alkaline phosphatases expressed in secB⁺ (AW1043) and secB mutant (CK1953) cells. The positions of the precursor (p) and mature (m) forms of alkaline phosphatase are indicated. (C) Quantification of the extent of processing of the mutant alkaline phosphatases from the experiment depicted in panel B. Darkly shaded bars represent the extent of processing in the secB⁺ strain and hatched bars represent processing in the secB mutant strain.