Effect of amino acid substitutions in the signal peptide cleavage region on the processing of escherichia coli alkaline phosphatase

A wide range (69) of mutant Kt,chtnchia coh alkaline phosphatases (PhoA) with various single ami no acid substitutions ai positions from > îo \-\ of the signal peptide (SP) were obtained to .study tIJP protein processing as a function of the cleavage .site sequence. Amber suppressor mutagenesis was used included: (i) introduction of amber mutations into the corresponding positions, and (ii) expression of the mutant, genes in K.roh strains producing amber-suppressor tRNAs specific to Her, Gin. Tyr. Leu, Ala. Glu, Plie. (îly. His, Cys, Lys and Pro. The processing of the mutant was assayed in pulse chase experiments in vivo. The results gave a new expérimental support for the (-3, -1 )-rule. The data also reveals a higher amino acids conservation at -1 position of Gram-negative bacteriaas compared with the eukaryotir organisms. The efficient processing was provided by medium-size residues at position .r). This suggests that the size of residues not only at positions -1 and II, as it was revealed earlier, but also at position -5 effects the processing rate. Hased on the stereochemical analysis we suggest a conformation of the 5 to 1 region of SP in the SPase binding pocket thai is consistent with the mutagenesis and statistical data. I'hr authors ijrattfnlly acknowlfdgf support by fhf Swint \dtirmal Scirnrt Foundation (grant 7Sl:I'JOJMjQ!.