9.A.4 The YggT or Fanciful K+ Uptake-B (FkuB; YggT) Family

Nakamura et al. (1996) identified a DNA fragment from Vibrio alginolyticus which complemented the growth defect of a K+ uptake deficient mutant of E. coli TK420. Two of the residing genes on this fragment were reported to be required for growth in synthetic medium containing 10 mM K+ and 100 mM Na+. K+ uptake was restored by introducing these genes.

Homologues of FkuB (most of 180-200 aas or of 80-100 aas) include the E. coli YggT protein. The larger members of this family contain a repeat found in many integral membrane proteins; the smaller members have just one.

In the E. coli YggT protein (188 aas), residues 1-91 are repeated (92-182). Half sized homologues (e.g., the YggT homologues of Geobacter uraniumreducens; 105 aas; gi#88936025, and Bacillus anthracis; YlmG; 87 aas; gi#49180675, both have just 2 TMSs). Other homologues are much larger with more than four TMSs (e.g., from Wolbachia; 992 aas; 6-8 putative TMSs with a large N-terminal hydrophilic domain and a smaller C-terminal hydrophilic domain) and the Type IV secretory pathway VirB6 component of Wolbachia (gi#58585051; 1040 aas; 8 putative TMSs with a long hydrophilic N-terminus of >600 aas).

The proposed transport function catalyzed by FkuB is:

K+ (out) → K+ (in)



Nakamura, T., Y. Katoh, Y. Shimizu, Y. Matsuba, and T. Unemoto. (1996). Cloning and sequencing of novel genes from Vibrio alginolyticus that support the growth of K+ uptake-deficient mutant of Escherichia coli. Biochim. Biophys. Acta 1277: 201-208.


TC#NameOrganismal TypeExample
9.A.4.1.1The 185 aa, 4 putative TMS K+ uptake protein, FkuBBacteriaFkuB of Vibrio alginolyticus (P52059)
9.A.4.1.2The 188 aa, 4 putative TMS YggT protein of unknown functionBacteriaYggT of E. coli (P64564)

TC#NameOrganismal TypeExample
9.A.4.2.1The 87 aa 2 putative TMS YlmG protein of unknown functionBacteriaYlmG of Bacillus anthracis (gi #49180675)

YggT family member of 181 aas

Red Algae

YggT homologue of Galdieria sulphuraria


YggT family protein of 157 aas


YggT homologue of Galdieria sulphuraria


Uncharacterized protein of 193 aas and 4 TMSs.


UP of Treponema pedis


TC#NameOrganismal TypeExample

The 992 aa 6-8 putative TMS protein (PfamPF04610 family), TrbL


TrbL of Wolbachia endosymbiont of Drosophila melanogaster (gi #42410430)