Table 3.

Suppression of btuB L8P and V10P mutations by Cys substitutions in TonBa

Plasmid or plasmid-encoded substitutionConcn of CN-Cbl for maximal growth (nM) of strain carrying:
tonBb btuBc
pBtuB+pL8PpV10P
pSU19>5,0000.55,0005,000
pTonB0.50.51,0005,000
pExbBD>5,0000.55,0005,000
pTonBExbBD0.50.51,0005,000
C18A0.50.55005,000
N159C0.50.550050
Q160C0.50.50.50.5
P161C0.50.51,0005,000
Q162C0.50.55050
Y163C0.50.51,0005,000
P164C0.50.55005,000
  • a Concentrations of CN-Cbl affording colony sizes comparable to that on methionine-supplemented medium are reported as in Table 1.

  • b The indicated tonB plasmids were introduced into the tonB strain RK5043 to evaluate their ability to complement the defect in CN-Cbl utilization. No btuB-carrying plasmid was present.

  • c The indicated plasmids were introduced intobtuB strain RK5016 in combination with compatible plasmid pAG1 derivatives carrying the wild-type btuB gene or the L8P- or V10P-encoding alleles, as indicated.