TABLE 1

Properties of initial amtB mutant strains

Strain no. NCMamtB mutationDoubling timea (min)MA uptake [pmol/(ml × OD600 × min)]Location in sequenceLocation in structure
3722None50100
4310Null∼210b≤7c
4199C-terminal delete (ΔC-term)d11025C-terminalC-terminal
4275Frameshifte160b≤7C-terminalC-terminal
4237G393A∼190b≤7C-terminalContact with loop 1
4238L394A∼190b≤7C-terminalContact with loops 1 and 3
4193G393A L394A (double)∼190b≤7C-terminalContact with loops 1 and 3
4348E121A∼190b≤7Loop 3Contact with loops 1 and 5 and C-terminal
4349R122A∼190b≤7Loop 3Contact with loops 5 and 9 and C-terminal
4326K184A50100Loop 5No contacts
4327R185A∼190b≤7Loop 5Contact with loops 1, 3, 5, 9, and C-terminal
4344K190A50100Loop 5No contacts
4346E191A7085Loop 5Contact with C-terminal
4350K255A14010Loop 7Contact with C-terminal of adjacent monomer
  • a Minimal medium, pH 5.5, containing 0.5 mm NH4+ and 0.1% glucose.

  • b Initial doubling time. Doubling time increases as ammonium is consumed. See Figure 1, A and B.

  • c Detection limit.

  • d AmtB lacking its last 24 residues. G382 is changed to A, the normal C-terminal residue. See materials and methods.

  • e The protein sequence of the wild-type C terminus, beginning with residue 381 and ending with the last residue, A406, is VGLRVPEEQEREGLDVNSHGENAYNA. The protein sequence of the frameshift C terminus, which is shortened by two residues, is VGLRVPEEQERESGGCQQPRRECL. Residues following the frameshift are in boldface type.