FIG. 3.

Defective release of precursors from SecBL75Q is suppressed by overproduction of SecA. Cells were grown in M63 minimal maltose-glycerol medium containing ampicillin. Cells were pulse-labeled with Tran³⁵S-label for 15 s, and the label was chased with nonradioactive methionine. Samples were taken after the pulse and after 1 and 2 min of chase. Cells were extracted, and the extract was subjected to anti-SecB affinity chromatography as described in Materials and Methods. Proteins bound to the column were eluted and analyzed by SDS-PAGE (12.5% polyacrylamide) and fluorography. Samples were as follows: lane a, HAC50 (secB⁺/pBR322), 15-s pulse; lane b, HAC50, 1-min chase; lane c, HAC50, 2-min chase; lane d, HAC52 (secBL75Q/pBR322), 15-s pulse; lane e, HAC52, 1-min chase; lane f, HAC52, 2-min chase; lane g, HAC53 (secBL75Q/pMF8), 15-s pulse; lane h, HAC53, 1-min chase; lane i, HAC53, 2-min chase. The numbers at the right are molecular weight markers (in thousands). The mobilities of SecB (B), proOmpA (O), preMBP (M), and preLamB (L) are indicated on the left.