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Gene Review

lacY  -  lactose permease

Escherichia coli str. K-12 substr. MG1655

Synonyms: ECK0340, JW0334
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Disease relevance of lacY


High impact information on lacY

  • Moreover, even when an odd number of helices is deleted, the C terminus remains on the cytoplasmic surface of the membrane, as judged by lacY-phoA fusion analysis [4].
  • Stop codons (TAA) have now been substituted sequentially for amino acid codons 396-401 in the lacY gene, and the termination mutants were expressed from the plasmid pT7-5 [5].
  • By using restriction fragments of lacY genes harboring specific site-directed mutations, a fusion gene has been constructed that encodes a permease in which His-35 and His-39 are replaced with arginine, and His-205 with glutamine (RQHE permease) [6].
  • Arg-302, His-322, and Glu-325, neighboring residues in putative helices IX and X of the lac permease (lacY gene product) of Escherichia coli, play an important role in lactose/H+ symport, possibly as components of a catalytic triad similar to that postulated for the serine proteases [Kaback, H. R. (1987) Biochemistry 26, 2071-2076] [6].
  • The lac operon of Escherichia coli spans approximately 5300 base pairs and includes the lacZ, lacY, and lacA genes in addition to the operator, promoter, and transcription termination regions [7].

Chemical compound and disease context of lacY


Biological context of lacY


Associations of lacY with chemical compounds

  • Coexpression of lacY gene fragments encoding the first two transmembrane domains and the remaining 10 transmembrane domains complement in the membrane and catalyze active lactose transport [Wrubel, W., Stochaj, U., et al. (1990) J. Bacteriol. 172, 5374-5381] [14].
  • Imprecise excision was monitored by selecting for melibiose+ (Mel+) phenotype, which requires only a functioning lacY gene [15].
  • (ii) Recombinant C. glutamicum cells bearing the lacY gene displayed an increased influx of o-nitrophenyl-beta-D-galactopyranoside, which was inhibited by N-ethylmaleimide [16].
  • Although studies on DNA microarrays revealed apparent cross-regulation of gene expression between galactose and lactose metabolism in the Stock Center isolate of MG1655, this was due to the occurrence of mutations that increased lacY expression and suppressed slow growth on galactose [17].
  • Sequencing of the mutant lacY gene revealed a point mutation resulting in the substitution of glycine-159 by a cysteine residue [18].

Other interactions of lacY

  • Very little lacYA and lacY mRNAs were present, whereas in cells induced to steady state, there was 10 times more lacZ than lacZYA mRNA [19].

Analytical, diagnostic and therapeutic context of lacY

  • The mutants were constructed by site-directed mutagenesis such that stop codons were placed at specified positions, and the altered lacY genes were expressed at a relatively low rate from plasmid pACYC184 [20].
  • As judged by [35S]methionine labeling and immunoblotting, intact permease is completely absent from the membrane of cells expressing lacY fragments either individually or together [21].
  • PCR was used to amplify the lacY DNA of each mutant, which was then sequenced by the Sanger method [22].


  1. Sequence of the lactose permease gene. Büchel, D.E., Gronenborn, B., Müller-Hill, B. Nature (1980) [Pubmed]
  2. Nucleotide sequence of Klebsiella pneumoniae lac genes. Buvinger, W.E., Riley, M. J. Bacteriol. (1985) [Pubmed]
  3. The effect of the lacY gene on the induction of IPTG inducible promoters, studied in Escherichia coli and Pseudomonas fluorescens. Hansen, L.H., Knudsen, S., Sørensen, S.J. Curr. Microbiol. (1998) [Pubmed]
  4. Organization and stability of a polytopic membrane protein: deletion analysis of the lactose permease of Escherichia coli. Bibi, E., Verner, G., Chang, C.Y., Kaback, H.R. Proc. Natl. Acad. Sci. U.S.A. (1991) [Pubmed]
  5. Sequential truncation of the lactose permease over a three-amino acid sequence near the carboxyl terminus leads to progressive loss of activity and stability. McKenna, E., Hardy, D., Pastore, J.C., Kaback, H.R. Proc. Natl. Acad. Sci. U.S.A. (1991) [Pubmed]
  6. lac permease of Escherichia coli containing a single histidine residue is fully functional. Püttner, I.B., Kaback, H.R. Proc. Natl. Acad. Sci. U.S.A. (1988) [Pubmed]
  7. DNA sequence of the lactose operon: the lacA gene and the transcriptional termination region. Hediger, M.A., Johnson, D.F., Nierlich, D.P., Zabin, I. Proc. Natl. Acad. Sci. U.S.A. (1985) [Pubmed]
  8. Polarity effects in the lactose operon of Escherichia coli. Li, Y., Altman, S. J. Mol. Biol. (2004) [Pubmed]
  9. Interaction of pyridostigmine bromide and N,N-diethyl-m-toluamide alone and in combination with P-glycoprotein expressed in Escherichia coli leaky mutant. El-Masry, E.M., Abou-Donia, M.B. J. Toxicol. Environ. Health Part A (2006) [Pubmed]
  10. Variable coordination of cotranscribed genes in Escherichia coli following antisense repression. Dryselius, R., Nikravesh, A., Kulyt??, A., Goh, S., Good, L. BMC Microbiol. (2006) [Pubmed]
  11. lac permease of Escherichia coli: topology and sequence elements promoting membrane insertion. Calamia, J., Manoil, C. Proc. Natl. Acad. Sci. U.S.A. (1990) [Pubmed]
  12. Yersinia pestis lacZ expresses a beta-galactosidase with low enzymatic activity. Bobrov, A.G., Perry, R.D. FEMS Microbiol. Lett. (2006) [Pubmed]
  13. The interaction between aspartic acid 237 and lysine 358 in the lactose carrier of Escherichia coli. King, S.C., Hansen, C.L., Wilson, T.H. Biochim. Biophys. Acta (1991) [Pubmed]
  14. Helix packing in the lactose permease of Escherichia coli determined by site-directed thiol cross-linking: helix I is close to helices V and XI. Wang, Q., Kaback, H.R. Biochemistry (1999) [Pubmed]
  15. DNA rearrangements associated with reversion of bacteriophage Mu-induced mutations. Khatoon, H., Bukhari, A.I. Genetics (1981) [Pubmed]
  16. Lactose permease of Escherichia coli catalyzes active beta-galactoside transport in a gram-positive bacterium. Brabetz, W., Liebl, W., Schleifer, K.H. J. Bacteriol. (1993) [Pubmed]
  17. Physiological studies of Escherichia coli strain MG1655: growth defects and apparent cross-regulation of gene expression. Soupene, E., van Heeswijk, W.C., Plumbridge, J., Stewart, V., Bertenthal, D., Lee, H., Prasad, G., Paliy, O., Charernnoppakul, P., Kustu, S. J. Bacteriol. (2003) [Pubmed]
  18. Characterization and sequencing of an uncoupled lactose carrier mutant of Escherichia coli. Matos, M.E., Wilson, T.H. Biochem. Biophys. Res. Commun. (1994) [Pubmed]
  19. Transcription and decay of the lac messenger: role of an intergenic terminator. Murakawa, G.J., Kwan, C., Yamashita, J., Nierlich, D.P. J. Bacteriol. (1991) [Pubmed]
  20. A five-residue sequence near the carboxyl terminus of the polytopic membrane protein lac permease is required for stability within the membrane. Roepe, P.D., Zbar, R.I., Sarkar, H.K., Kaback, H.R. Proc. Natl. Acad. Sci. U.S.A. (1989) [Pubmed]
  21. In vivo expression of the lacY gene in two segments leads to functional lac permease. Bibi, E., Kaback, H.R. Proc. Natl. Acad. Sci. U.S.A. (1990) [Pubmed]
  22. Lactose carrier mutants of Escherichia coli with changes in sugar recognition (lactose versus melibiose). Varela, M.F., Brooker, R.J., Wilson, T.H. J. Bacteriol. (1997) [Pubmed]
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