Evidence that the folate-dependent proteins YgfZ and MnmEG have opposing effects on growth and on activity of the iron-sulfur enzyme MiaB

J Bacteriol. 2012 Jan;194(2):362-7. doi: 10.1128/JB.06226-11. Epub 2011 Nov 11.


The folate-dependent protein YgfZ of Escherichia coli participates in the synthesis and repair of iron-sulfur (Fe-S) clusters; it belongs to a family of enzymes that use folate to capture formaldehyde units. Ablation of ygfZ is known to reduce growth, to increase sensitivity to oxidative stress, and to lower the activities of MiaB and other Fe-S enzymes. It has been reported that the growth phenotype can be suppressed by disrupting the tRNA modification gene mnmE. We first confirmed the latter observation using deletions in a simpler, more defined genetic background. We then showed that deleting mnmE substantially restores MiaB activity in ygfZ deletant cells and that overexpressing MnmE with its partner MnmG exacerbates the growth and MiaB activity phenotypes of the ygfZ deletant. MnmE, with MnmG, normally mediates a folate-dependent transfer of a formaldehyde unit to tRNA, and the MnmEG-mediated effects on the phenotypes of the ΔygfZ mutant apparently require folate, as evidenced by the effect of eliminating all folates by deleting folE. The expression of YgfZ was unaffected by deleting mnmE or overexpressing MnmEG or by folate status. Since formaldehyde transfer is a potential link between MnmEG and YgfZ, we inactivated formaldehyde detoxification by deleting frmA. This deletion had little effect on growth or MiaB activity in the ΔygfZ strain in the presence of formaldehyde, making it unlikely that formaldehyde alone connects the actions of MnmEG and YgfZ. A more plausible explanation is that MnmEG erroneously transfers a folate-bound formaldehyde unit to MiaB and that YgfZ reverses this.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Escherichia coli / genetics
  • Escherichia coli / growth & development*
  • Escherichia coli / metabolism
  • Escherichia coli Proteins / genetics
  • Escherichia coli Proteins / metabolism*
  • Folic Acid / metabolism*
  • Formaldehyde / metabolism
  • GTP Phosphohydrolases / genetics
  • GTP Phosphohydrolases / metabolism*
  • Gene Expression Regulation, Bacterial / physiology
  • One-Carbon Group Transferases / genetics
  • One-Carbon Group Transferases / metabolism*
  • Sulfurtransferases / genetics
  • Sulfurtransferases / metabolism*


  • Carrier Proteins
  • Escherichia coli Proteins
  • YgfZ protein, E coli
  • Formaldehyde
  • Folic Acid
  • MnmG protein, E coli
  • One-Carbon Group Transferases
  • MiaB protein, E coli
  • Sulfurtransferases
  • GTP Phosphohydrolases
  • MnmE protein, E coli