Determinants for protein localization: beta-lactamase signal sequence directs globin across microsomal membranes.

Abstract

A hybrid gene containing 182 codons of Escherichia coli .beta.-lactamase at the amino terminus of the corresponding protein and 141 codons of .alpha.-globin at the carboxyl terminus was generated by inserting chimpanzee .alpha.-globin c[complementary]DNA into the Pst I site of plasmid pBR322. RNA transcribed in vitro from this plastid gave a corresponding hybrid protein in a wheat germ cell-free translation system. The hybrid protein was protected from tryptic digestion and the pre-.beta.-lactamase signal peptide was removed when dog pancreas membrane vesicles were present during translation. A deletion mutant containing 23 codons of pre-.beta.-lactmase signal sequence and 5 codons of mature .beta.-lactamase fused to the .alpha.-globin cDNA gave a shorter hybrid protein that behaved similarly. A mutation that removed essentially all of the pre-.beta.-lactamase sequence gave a protein that was neither protected nor processed. At most, only the signal peptide and the 5 amino acids of .beta.-lactamase were necessary to convert .alpha.-globin (a cytoplasmic protein) into a secretory protein.