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Synonyms: MelR, MelR-melibiose |
Summary:
MelR, "melibiose regulator," is a transcription factor involved in disaccharide melibiose degradation. It coregulates with CRP, a global transcriptional regulator [1, 5, 9] These regulators bind cooperatively to activate transcription of the operon involved in transport and catabolism of melibiose. Synthesis of this operon is induced when Escherichia coli is grown on melibiose in the absence of glucose. Gene induction occurs when the physiological inducer, melibiose, binds to the MelR regulator and when cellular cyclic AMP levels are high. In the presence of melibiose, MelR binds in tandem to repeat sequences in the melR/melAB intergenic region to activate transcription by overlapping the -35 box of the promoter melAp. The binding targets for MelR consist of 18-nucleotide-long repeat sequences that possess conserved motifs; each monomer binds to one of these conserved sequences [1, 5, 7] MelR binds to five target sites in the melAp region. MelR binds to the less-conserved site (-42.5) with less strength; this binding occurs only in the presence of melibiose, and it is absolutely required for expression of melAp [1] MelR binding to the distal site (-237.5) has been shown to down-regulate the expression of melRp and melAp [3, 4] In the absence of melibiose, MelR is unable to activate melAp, but it regulates its own expression by repressing melRp and melAp simultaneously [1, 10, 11] Melibiose triggers MelR-dependent activation of melAp and relieves MelR-dependent repression of melRp [10, 11] The melAB operon is located upstream of melR and in the opposite direction. This regulator belongs to the AraC/XylS family of activators and occurs as both a monomer and a homodimer. Read more > |
Transcription factor | ![]() ![]() |
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TF conformation(s): |
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Evolutionary Family: | AraC/XylS | |||||||||||||||||||||
TFBs length: | 18 | |||||||||||||||||||||
TFBs symmetry: | asymmetric | |||||||||||||||||||||
Sensing class: | Sensing external and internal signals | |||||||||||||||||||||
Connectivity class: | Local Regulator | |||||||||||||||||||||
Gene name: | melR | |||||||||||||||||||||
Genome position: | 4340720-4341628 | |||||||||||||||||||||
Length: | 909 bp / 302 aa | |||||||||||||||||||||
Operon name: | melR | |||||||||||||||||||||
TU(s) encoding the TF: |
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Regulon |
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Regulated gene(s) | melA, melB, melR | ||||||
Multifun term(s) of regulated gene(s) |
MultiFun Term (List of genes associated to the multifun term)
carbon compounds (3)
Porters (Uni-, Sym- and Antiporters) (1)
membrane (1)
Transcription related (1)
activator (1)
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Regulated operon(s) | melAB, melR | ||||||
First gene in the operon(s) | melA, melR | ||||||
Simple and complex regulons | CRP,MelR | ||||||
Simple and complex regulatory phrases | Regulatory phrase (List of promoters regulated by the phrase) |
Transcription factor regulation |
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Alignment and PSSM for MelR TFBSs | ![]() |
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Aligned TFBS of MelR |
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Sequence | |
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ATTCCCATAAACTCAGATTTA | |
ATTACCTGAAAAGCAGAGTTT | |
ATTCCCATAAACTCAGATCCT | |
TTTCCTGGAATATCAGAATTA | |
TCAACCTGGAAGCCGGAGGTT |
Position weight matrix (PWM). MelR matrix-quality result |
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A 3 0 1 2 0 0 2 0 4 5 4 2 0 0 4 0 5 1 0 0 2 C 0 1 0 3 5 4 0 0 0 0 0 2 1 5 0 0 0 0 1 1 0 G 0 0 0 0 0 0 1 3 1 0 0 1 1 0 1 5 0 2 1 0 0 T 2 4 4 0 0 1 2 2 0 0 1 0 3 0 0 0 0 2 3 4 3 |
Consensus |
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; consensus.strict attcCCagaAactCaGAgttt ; consensus.strict.rc AAACTCTGAGTTTCTGGGAAT ; consensus.IUPAC wttmCCwkaAamtCaGAkttw ; consensus.IUPAC.rc WAAMTCTGAKTTTMWGGKAAW ; consensus.regexp [at]tt[ac]CC[at][gt]aAa[ac]tCaGA[gt]tt[at] ; consensus.regexp.rc [AT]AA[AC]TCTGA[GT]TTT[AC][AT]GG[GT]AA[AT] |
Evolutionary conservation of regulatory elements | ![]() |
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Reference(s) |
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