| Abstract: | The deletion of several codons within the signal sequence coding region of the Escherichia coli lipoprotein gene has been accomplished by oligonucleotide-directed site-specific mutagenesis. The deletion of the Leu-13 residue in a mutant in which two glycine residues had previously been deleted from the hydrophobic region (Inouye, S., Vlasuk, G., Hsiung, H., and Inouye, M. (1984) J. Biol. Chem. 259, 3729-3733) was found to cause the accumulation of the unmodified form of the protein in the cytoplasm and cytoplasmic membrane. This mutation also caused a cessation in cell growth within 15 min after synthesis of the mutant protein was induced. A deletion of the Val-7 residue was capable of suppressing the effect of the Leu-13 deletion when both are present. However, by itself the Val-7 deletion appeared to have little effect on the glycine mutant. The ability of the signal sequence to mediate the secretion of the protein after the deletion of 4 residues from the hydrophobic region demonstrates a surprising degree of flexibility in the length of this region. The deletion mutations were also found to have an unusual effect on the rate of synthesis of lipoprotein. |
