​tcdb.​org). To establish homology (common ancestry), either between two proteins or between two internal segments in a set of homologous proteins, the SSearch, IC and GAP programs were initially used [13, 14, 21, 35]. To establish homology among putative full-length homologues or repeat sequences of greater than 60 amino acyl residues, a value of 10 standard deviations (S.D.) was considered sufficient [4, 18]. According to Dayhoff et al.[36], this

value corresponds to a probability of 10-24 that this degree of similarity arose by chance [36]. We have found that a single iteration with a cut-off value of e-4 for the initial BLAST search, and a cut-off value of e-5 for the EX 527 chemical structure second iteration, reliably retrieves homologues with few false positives. Nevertheless, all proteins giving BLAST e-values of e-7 or larger were tested for homology using the GAP program with default settings, requiring a comparison score of at least 10 S.D. in order to conclude that these proteins share a common origin. All hits that satisfied these criteria were put through a modified CD-Hit program with a 90% cut-off value [13, 24] to eliminate redundancies, fragmentary sequences and sequences with greater that 90% identity with a kept protein. gi-Extract Angiogenesis inhibitor from TCDB was used to extract the gi numbers of homologues, which were then searched through

NCBI to obtain the FASTA sequences. A multiple alignment

was generated with the ClustalW2 program, and homology of all aligned sequences throughout the relevant transmembrane domains was established using the SSearch and GAP programs [13, 21, 35]. Internal regions were examined for repeats whose dissimilar segments were compared with potentially homologous regions of the same proteins using the Phosphatidylinositol diacylglycerol-lyase SSearch and GAP programs with default settings. The ATP hydrolyzing (ABC) domains of these systems were excluded, and only the transmembrane domains or proteins were used in the analyses. Topological analyses Average hydropathy, amphipathicity and similarity plots for multiply aligned sets of homologues were generated with the AveHAS program [37], while web-based hydropathy, amphipathicity and predicted topology for an individual protein were estimated using the WHAT program [25] as well as the TMHMM 2.0 [38], HMMTOP [29], and TOPCONS [topcons.cbr.su.se/] programs. Some of these programs were updated as described by Yen et al.[13, 21]. Sequences were spliced for statistical analyses as described by Zhou et al.[15]. The global alignment program with displayed TMSs (GAP-DT), in combination with the SSearch and GAP programs, was used to determine where an extra transmembrane Smoothened antagonist domain might have been inserted into or added to a transporter of a smaller number of TMSs to give rise to a transporter with a larger number of TMSs.