%0 Journal Article %A van Dijl, Jan Maarten %A de Jong, Anne %A Smith, Hilde %A Bron, Sierd %A Venema, Gerard %T Non-functional expression of Escherichia coli signal peptidase I in Bacillus subtilis %D 1991 %J Microbiology, %V 137 %N 9 %P 2073-2083 %@ 1465-2080 %R https://doi.org/10.1099/00221287-137-9-2073 %I Microbiology Society, %X The Escherichia coli lep gene, encoding signal peptidase I (SPase I) was provided with Bacillus subtilis transcription/translation signals and expressed in this organism. When present on a low-copy-number plasmid, the amount of E. coli SPase I produced (per mg cell protein) in B. subtilis was half that produced in wild-type E. coli cells. The production of E. coli SPase I in B. subtilis was increased approximately fivefold by cloning the lep gene into a high-copy-number plasmid. The expression of E. coli SPase I in B. subtilis did not appear to increase the rate of processing of two hybrid secretory precursor proteins. Two observations may explain the failure of E. coli SPase I to stimulate processing of exported proteins in B. subtilis. First, the E. coli SPase I was apparently not exposed on the outside of the B. subtilis cytoplasmic membrane, indicating its incorrect insertion into the membrane. Second, in vitro processing studies, using cell-free extracts of B. subtilis producing E. coli SPase I, suggested that the enzyme was not active. A further outcome of this study was that conditions favouring processing of precursors by SPase I in cell-free extracts of E. coli did not favour processing by the corresponding enzyme in B. subtilis cell-free extracts. This suggests that significant differences exist between the two enzymes. The observation that antibodies directed against E. coli SPase I did not cross-react with B. subtilis membrane proteins supports this idea. %U https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-137-9-2073