Figure 5.

In RseP⁻ cells, as the number of leucines in Ala/Leu segments increase from 5 leucines to 10, there is a steady shift of the fragments toward the insoluble fraction from the soluble fraction; the major break point occurred at 7–8 leucines. The RseP⁻ condition prevents further processing of TM segments after SPase I cleavage, which reveals information about the inherent stability of TM segments. The important conclusion from these data is that the hydrophobicity requirements for partitioning a segment from translocon to membrane are different than for partitioning between membrane and the cytoplasm; 4 leucines are sufficient to guarantee translocon-to-bilayer partitioning of the H-segment (Figure 2) whereas 7 or so are required to prevent the CadC-H protein from dropping into the cytoplasm. See Material and Methods for experimental details.