Figure 1.

Localization of the components of the E. coli SRP/SRP receptor in the cell-free integration system used. Immunoblot of the fractions indicated using rabbit antisera directed against Ffh (P48) and FtsY and a horseradish peroxidase-based enhanced chemiluminescence (ECL) detection system (Amersham). The same blot was subsequently probed with both antisera. One equivalent (eq) of a particular fraction is the amount used per 25 μl cell-free synthesis reaction. For P48–6His and FtsY, 1 eq corresponds to ∼0.2 and 0.5 μg protein, respectively. The molecular nature of the lower band detected by the FtsY antiserum even in FtsY-free samples is unknown. INV, Inside-out inner membrane vesicles; U-INV, urea-treated INV; FtsY⁻-INV, INV prepared from a conditional FtsY-mutant strain; CTF, cytosolic translation factors, prepared either from wild-type E. coli cells (wt-CTF) or from the conditional ftsY-mutant (FtsY⁻-CTF).