Fig. 1. The isolation of a deletion allele within the C. elegans plexin 1 locus. (A) A deletion allele of Ce-plx-1 was isolated from a mutagenized C. elegans N2 strain frozen library screened using a PCR based method (see Materials and methods). The genomic DNA deletion removes all of exon 19 (red dotted rectangle), which encodes the transmembrane domain. (B) The plx-1 genomic DNA sequence was used to design primers to PCR amplify multiple cDNAs that were sequenced and assembled into a full-length clone. The cDNA from plx-1(ev724) was sequenced and revealed abnormal splicing between exons 18 and 20 resulting in a frame-shift mutation. (C) The intracellular portion of C. elegans PLX-1 is highly conserved with human and Drosophila plexins. In particular, the seven residue region (black underline) responsible for RAC^GTP binding in Drosophila Plexin B is well conserved in Drosophila Plexin A, C. elegans PLX-1 and PLX-2, and human plexins A3, B1 and C1. The RHO-binding region defined for Drosphila Plexin B (red underline) is less well conserved, as a large portion of it is missing in plexins from other species. However, the amino acids bordering this region are well aligned in plexins from C. elegans, Drosophila and human. The alignment includes Hm-PLX-A3 (X87852), Hm-PLX-B1 (X87904), Hm-PLX-C1 (AF030339), Dm-PLX-A (T13937), Dm-PLX-B (T13164), Ce-PLX-1 (NP_500018) and Ce-PLX-2 (NP_497001).