TABLE 2

Amino acid, nonsynonymous, and synonymous substitutions in orthologous rodent odorant receptors, by segment

NORs (N = 8)TORs (N = 10)
SegmentNAADIFPDIFKAKSKA/KSNAADIFPDIFKAKSKA/KS
All sequences
TM1a126140.110.0610.180.3410460.060.0270.270.10
IC12410.040.0160.310.05200.000.0000.270.00
TM211520.020.0090.180.059230.030.0160.190.09
EC194100.110.0640.340.197250.070.0330.070.45
TM311990.080.0400.220.199610.010.0080.260.03
IC27640.050.0220.160.141040.000.0040.240.02
TM4a208360.170.0920.180.51267180.070.0360.190.20
EC2263120.050.0210.210.10330140.040.0220.110.21
TM5175110.060.0300.180.17220120.060.0270.220.12
IC3a170190.110.0620.190.3225490.040.0190.220.09
TM612010.010.0040.110.0418020.010.0080.110.07
EC34830.060.0360.220.166320.030.0250.170.14
TM79840.040.0200.310.0611010.010.0080.340.03
All16361260.080.0400.200.201912730.040.0200.190.11
NORs (N = 5)TORs (N = 8)
SegmentNAADIFPDIFKAKSKA/KSNAADIFPDIFKAKSKA/KS
Restricted sample (KS ≤ 0.2)
TM1a7470.090.0450.140.32780.000.0000.280.00
IC1140.000.0000.250.00150.000.0000.200.00
TM2690.000.0000.120.006910.010.0080.260.03
EC15830.050.0250.240.105420.040.0170.060.29
TM37110.010.0060.190.037210.010.0110.250.04
IC2450.000.0000.130.00800.000.0060.240.03
TM4a127120.090.0490.130.3921360.030.0140.140.10
EC216440.020.0100.150.0726460.020.0140.090.15
TM510940.040.0180.190.1017660.030.0180.190.10
IC3a113110.100.0540.160.3420730.010.0090.220.04
TM6800.000.0000.080.0016020.010.0060.100.06
EC33220.060.0370.200.195520.040.0280.170.16
TM75830.050.0280.230.129010.010.0050.280.02
All1014470.050.0230.160.151533300.020.0110.170.07

Rows summarize amino acid and nucleotide substitutions within individual structural domains of the odorant-receptor protein, for all of the ortholog pairs sampled from a given tissue. Transmembrane (TMx), intracellular (ICx), and extracellular (ECx) domains are listed as they occur topologically in the primary structure of the protein; the poorly conserved amino- and carboxyl-terminal tails are omitted. For each domain, the columns give total numbers of codons compared (NAA), raw numbers of amino acid differences (DIF), proportion of amino acid differences (PDIF), and estimated rates of nonsynonymous and synonymous substitution (KA, KS, and their ratio KA/KS). Data for NORs and TORs are summarized separately in the left-hand and right-hand sides, respectively. The top summarizes data for all 18 genes (8 NORs and 10 TORs). The bottom excludes 3 NORs and 2 TORs for which KS > 0.2; these genes are presumably the ones at greatest risk of being represented by mouse and rat sequences that are paralogous rather than orthologous (see Table 1).

  • a Relative rates of amino acid substitution are strikingly higher for NORs than for TORs in these domains, but not in any other domains with large numbers of sampled codons. The first five and last three domains are represented by fewer genes (and hence relatively fewer codons) than the block from IC2 through IC3, because some genes in the data set are represented by partial sequences (Table 1).