GenePage for the cmoA gene of Escherichia coli K-12

Primary Gene Name: cmoA
EcoGene Accession Number: EG14033
K-12 Gene Accession Number: ECK1871
MG1655 Gene Identifier: b1870
Gene Name Mnemonic: CarboxylMethOxy
Alternate Gene Symbols: yecO
Description: Carboxy-SAM synthase
  # bp Upstream # bp Downstream
MW: 27776.64 ---------247 aa Pre-Run BlastP UniProt
Pre-Run BlastP NR+Env
Left End: 1952702
Left Intergenic Region

Name: yecN_cmoA

Length: 40 bp gap

Orientation: Codirectional+

Left_end: 1952662

Right_end: 1952701

Centisome: 42.07

Genomic Address
Minute or Centisome (%) = 42.07
Right End: 1953445
Right Intergenic Region

Name: cmoA_cmoB

Length: 4 bp overlap

Orientation: Codirectional+

Left_end: 1953442

Right_end: 1953445

Centisome: 42.09

The carboxy-SAM synthase CmoA utilizes prephenate as a carboxyl donor to synthesize carboxy-SAM, converting prephenate to phenylpyruvate and carbon dioxide; the departing prephenate hydroxyl group abstracts a proton from the S-methyl group of SAM generating water and a stabilized carbanion SAM ylide intermediate, which is then carboxylated by the carbon dioxide; prephenate is derived from chorismate; the carboxy-SAM co-factor is utilized by the CmoB tRNA (cmo5U34)-carboxymethyltransferase as the carboxymethyl donor (Kim, 2013). tRNAs from aroC and aroD mutants lack cmo5U and its methyl ester mcmo5U, implicating chorismate or a derivative in their synthesis (Björk, 1979; Björk, 1980; Hagervall, 1990). Two alternatives were proposed for the synthesis of cmo5U from ho5U in E. coli including the direct conversion by a carboxymethyltransferase (referred to as an acetylase) and a two-step reaction with mo5U as an intermediate; mo5U34 is present in the U wobble base of tRNAs from B. subtilis (Murao, 1978). CmoA, a member of the methyltrasferase superfamily, was previously thought to be involved in the chorismate-dependent conversion of mo5U34 to cmo5U34 in tRNA as both ho5U and mo5U accumulated in a cmoA mutant and in an aroD mutant, although a mechanism was not apparent; CmoB was previously thought to be responsible for the conversion of ho5U to mo5U since only ho5U accumulated in a cmoB mutants (Nasvall, 2004). Now it seems, since mo5U is not an intermediate in (m)cmo5U synthesis, that CmoB might utilize SAM inefficiently in the absence of CmoA-generated carboxy-SAM to form mo5U. Carboxy-SAM (Cx-SAM), also called S-adenosyl-S-carboxymethyl-l-homocysteine (SCM-SAH), was identified in crystal structures of E. coli and H. influenzae CmoA (Kim, 2013; Byrne, 2013). otherPDB (H. influenzae): 1IM8 (Lim, 2001). 4/128 CmoA(YecO) peptide masses from MS analysis confirm this start codon and indicate that the initial Met is not removed (Maillet, 2007). CmoA peptide masses from MS/MS analysis indicate this is the correct start site and that the initial Met is removed (Guo, 2014).

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