The modified secretory-trap vector incorporates a transmembrane (TM) domain, an internal ribosome entry site (IRES) and an alkaline phosphatase (PLAP) gene. Only the situation after insertion of this vector into a gene encoding a protein with a hydrophobic leader sequence (S) is shown. A bicistronic transcript is produced, encoding first a fusion between the endogenous protein and -geo that localizes to the neuronal cell body and second the PLAP protein, which localizes to the entire cell surface, including the axon.

Left Lower panel: (c) Modified secretory trap insertions into genes encoding proteins with hydrophobic leaders apparently result in fusion proteins that are inserted into membranes in a type I orientation (right) [12]. This places the –galactosidase domain of -geo (blue) in the cytosol, where it is more active than in fusions with leaderless proteins; the latter result in a type II orientation (left) with -galactosidase in the lumen of the endoplasmic reticulum (ER).

Right Lower panel: Expression of –geo (blue) and PLAP (purple) in a neuron.