Figure 1. A SEL-1 signal sequence :: green fluorescent protein (GFP) fusion (plasmid MTL-2/SIG/S65T) was expressed in C. elegans using an intestine-specific promoter,
mtl-2. (Freedman et al., 1993). Live animals immobilized with levamisole are shown (see Materials and Methods). GFP fluorescences green. Background autofluorescence of the intestine is yellow. (A) Diagram of the SEL-1::GFP fusion protein. The first 79 amino acids of SEL-1 are fused to the entire green fluorescent protein. The SEL-1 predicted signal sequence is shown as a black box. GFP is shown as a gray box. (B) An adult hermaphrodite expressing the SEL-1::GFP fusion. Strong green fluorescence is seen at the apical (small arrow) and basal surfaces of the intestinal membranes, and in pseudocoelomic spaces. The empty uterine spaces around unlaid embryos (dark structures) is filled with green fluorescent protein in the hermaphrodite shown (see large arrow). (C) An adult hermaphrodite expressing SEL-1 signal sequence :: GFP, in which fusion protein secreted into the pseudocoelomic space has been scavenged by a pair of coelomocytes (arrows) just anterior of the vulva. (D,E) Camera lucida drawings of B and C respectively, GFP fluorescence shown in green. L, lumen of intestine; U, uterine space; cc, coelomocyte.