THE MEMBRANE-BINDING C-TERMINUS OF PROTEIN-A FROM STAPHYLOCOCCUS-AUREUS AFFECTS ITS CELLULAR-LOCALIZATION AND CAUSES STRUCTURAL DEFORMATIONWHEN EXPRESSED IN ESCHERICHIA-COLI

Protein A from Staphylococcus aureus is a powerful diagnostic reagent and has several uses in human disease therapy. Expression in non-patho genic Escherichia coli containing recombinant plasmids coding for this protein has increased its availability, but can reduce the stability of the plasmid-bearing host. By employing immune electron microscopy, we have determined that E. coli containing stable plasmids coding for a truncated version of protein A, without the membrane binding site, s ecrete this protein through the cytoplasmic membrane and into the peri plasmic space, where it accumulates. E. coli containing unstable plasm ids, however, which code for the complete protein including the membra ne-binding site, target the protein into the cytoplasmic membrane. Thi s accumulation of protein A in the E. coli cytoplasmic membrane inhibi ts the formation of septa between dividing cells and results in aberra nt elongated, multi-chromosomal forms.