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Gene Review

melA  -  alpha-galactosidase, NAD(P)-binding

Escherichia coli str. K-12 substr. MG1655

Synonyms: ECK4112, JW4080, mel-7
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Disease relevance of melA

  • We analyzed gene expression of the melibiose operon of Escherichia coli using this plasmid, and found that a DNA fragment containing a large stem-loop structure with boxA sequence in it, which was present between melA and melB, caused strong reduction of gene expression [1].
  • The Rhizobium leguminosarum biovar phaseoli symbiotic plasmid pRP2JI carries a gene, melA, specifying the enzyme tyrosinase, which is responsible for the production of the pigment melanin in these bacteria [2].
  • In this framework, we characterized the melA gene for alpha-Gal in Lactobacillus plantarum [3].
  • Shewanella colwelliana D is a marine procaryote which produces a diffusible brown pigment that correlates with melA gene expression [4].
  • Upstream of melA, a putative galactoside transporter, designated RafP, was identified that shows high homology to LacS, the unique transporter for both alpha- and beta-galactosides in Streptococcus thermophilus. rafP is also expressed as a monocistronic mRNA [3].

High impact information on melA

  • The sequence data also supported the assumption that the mel locus forms an operon with melA in proximal position [5].
  • The nucleotide sequence data showed that melA codes for a 450 amino acid long protein with a molecular weight of 50.6 kd [5].
  • Following generation of a novel EcoRI restriction site in the intergenic sequence between the two genes of the mel operon by oligonucleotide-directed, site-specific mutagenesis, melA and melB were separately inserted into plasmid pT7-6 of the T7 expression system [6].
  • We show that melA is transcribed from its own promoter, yielding a monocistronic mRNA, and that it is regulated at the transcriptional level, i.e., it is induced by melibiose but is not totally repressed by glucose [3].
  • This first genetic characterization of melA and of its putative associated transporter, rafP, in a lactobacillus opens doors to various applications both in the manufacture of soy-derived products and in probiotic and nutraceutical issues [3].

Chemical compound and disease context of melA


Biological context of melA


Other interactions of melA

  • Both reporter enzyme activity and Northern hybridization analyses of dnaK and melA revealed a transcriptional induction, reaching its maximum when the culture was exposed to 0.75 M NaCl [8].


  1. Construction of a vector for the study of regulatory mechanism of gene expression and its utilization in the melibiose operon of Escherichia coli. Shimamoto, T., Noguchi, K., Kuroda, M., Tsuda, M., Tsuchiya, T. Nucleic Acids Symp. Ser. (1988) [Pubmed]
  2. Transcription of a Rhizobium leguminosarum biovar phaseoli gene needed for melanin synthesis is activated by nifA of Rhizobium and Klebsiella pneumoniae. Hawkins, F.K., Johnston, A.W. Mol. Microbiol. (1988) [Pubmed]
  3. Characterization of the melA locus for alpha-galactosidase in Lactobacillus plantarum. Silvestroni, A., Connes, C., Sesma, F., De Giori, G.S., Piard, J.C. Appl. Environ. Microbiol. (2002) [Pubmed]
  4. Homogentisic acid is the product of MelA, which mediates melanogenesis in the marine bacterium Shewanella colwelliana D. Coon, S.L., Kotob, S., Jarvis, B.B., Wang, S., Fuqua, W.C., Weiner, R.M. Appl. Environ. Microbiol. (1994) [Pubmed]
  5. Nucleotide sequence of the melA gene, coding for alpha-galactosidase in Escherichia coli K-12. Liljeström, P.L., Liljeström, P. Nucleic Acids Res. (1987) [Pubmed]
  6. Melibiose permease and alpha-galactosidase of Escherichia coli: identification by selective labeling using a T7 RNA polymerase/promoter expression system. Pourcher, T., Bassilana, M., Sarkar, H.K., Kaback, H.R., Leblanc, G. Biochemistry (1990) [Pubmed]
  7. The protein encoded by the Shewanella colwelliana melA gene is a p-hydroxyphenylpyruvate dioxygenase. Ruzafa, C., Solano, F., Sanchez-Amat, A. FEMS Microbiol. Lett. (1994) [Pubmed]
  8. Construction of a new reporter system to study the NaCl-dependent dnaK promoter activity of Lactobacillus sanfranciscensis. Hörmann, S., Vogel, R.F., Ehrmann, M. Appl. Microbiol. Biotechnol. (2006) [Pubmed]
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