Influence of the presence of the signal sequence on YedY expression in E. coli . (A) SDS PAGE of whole cell extracts or soluble extracts (25 μg) from E. coli BL21 (DE3) that harbor: (lane C-) an empty plasmid (negative control); (lane -SS) the plasmid pSM179 (which contains only the sequence encoding the mature protein); (lane + SS) the plasmid pSM189 (which contains both the mature protein sequence and the signal sequence). (B) Western blot analysis of the same samples with anti-histidine peroxidase conjugate antibodies. In lane -SS, the whole cell extract was diluted 200-fold to avoid saturation of the signal. MW: molecular weight standards.