Sil protein alignment and phylogenetic analysis. (a) Phylogenetic analysis of Sid-1-like proteins. The neighbor-joining tree is based on the alignment of the carboxy-terminal transmembrane domain corresponding to the TM2-TM11 region of C. elegans Sid-1 (Additional data files 1 and 4). Tc-SilC clusters with the human Sid-1-like proteins (SidT1 and SidT2), while Tc-SilA and Tc-SilB compose a distinct cluster. Orthology of these insect and vertebrate Sid-1-like proteins to the C. elegans homologs is unclear from this analysis. Proteins that contain the amino-terminal conserved region are indicated in red. (b) Two conserved regions in the amino-terminal extracellular domain. These regions are conserved in vertebrate Sid-1-like proteins (represented by human SidT1), insect Sil proteins (Tc-SilA), and C. elegans Tag-130, but not in C. elegans Sid-1.