TABLE 3.
Results of the McDonald-Kreitman testa
| ETEC fimbrial system component (protein)b | No. of polymorphic sites
|
No. of fixed sites
|
NIc | ||
|---|---|---|---|---|---|
| S | R | S | R | ||
| Chaperone (CfaA) | 121 | 110 | 83 | 85 | 0.89 |
| Major subunit (CfaB) | 120 | 111 | 27 | 31 | 0.81 |
| Outer membrane usher (CfaC) | 98 | 97 | 395 | 345 | 1.13 |
| Minor subunit (CfaE) | 53 | 91 | 170 | 195 | 1.50d |
a
Numbers of synonymous (S) and replacement (R) sites that are polymorphic within alleles of a subclass or that represent fixed differences between subclasses for each fimbrial component are shown. Under the neutral mutation theory, the S/R ratio should be equivalent for polymorphic and fixed sites under strict neutrality.
b
Protein function CFA/I homolog.
c
NI, neutrality index.
d
ΔG = 4.03; df = 1; P = 0.04 (two-tailed Fisher's exact test).