Table 1.

Phenotypes of proline substitutions in the BtuB Ton box

btuB alleleaCN-Cbl concn (nM) for maximal growthbTitercof:
ColE1ColE3BF23
Null>5,000RRR
WT0.5446
D6P0.5446
T7P0.5446
L8P>5,000446
V9P0.5446
V10P>5,000446
T11P0.5234
A12P0.5446
  • a The indicated btuB alleles were present in single gene copy at the chromosomal btuBlocus in strain RK8452. The alleles are designated by the corresponding amino acid substitution, numbered from the mature sequence. WT, wild type.

  • b Strains were streaked on minimal plates supplemented with required nutrients and serial 10-fold dilutions of CN-Cbl or l-methionine at 100 μg/ml. After the plates were incubated for 40 h at 37°C, the sizes of colonies were estimated, and the lowest concentrations of CN-Cbl allowing a colony size comparable to that on methionine-supplemented medium are reported.

  • c As described in Materials and Methods, serial 10-fold dilutions of the indicated colicins or phage were spotted onto cells in soft-agar layers on LB plates. The titers are the negative logs of the highest dilution of the agent that produces a zone of complete clearing. R, resistant to the highest concentration tested.