TABLE 1.
mal genes and their products, genes controlling mal gene expression, and genes related to maltodextrin metabolism
| Gene | Position on chromosome (min) | Gene product and function | Reference(s) |
|---|---|---|---|
| mal genes and their main regulator | |||
| malT | 76.5 | Transcriptional activator, essential for transcription of all mal genes except the malI/X/Y gene cluster. Binds ATP and maltotriose as inducer. | 34, 40, 66, 206, 214, 215, 280 |
| malE | 91.4 | Periplasmic MBP; binds maltose/maltodextrins with micromolar affinity. | 37, 76, 107–109, 128, 138, 244, 248, 257, 264, 265 |
| malF | 91.4 | Intrinsic membrane protein of the transport system. In association with MalG and MalK, it forms the MalFGK2 translocation complex. | 41, 80, 82, 93, 252, 273 |
| malG | 91.4 | Intrinsic membrane protein of the transport system. In association with MalF and MalK, it forms the MalFGK2 translocation complex. | 25, 50–52, 254, 273 |
| malK | 91.5 | Transport ATPase, responsible for energization of transport. In association with MalF and MalG, it forms the MalFGK2 translocation complex. Target of inducer exclusion by unphosphorylated EIIAGlc of the PTS. In the absence of inducer, it interacts with MalT to cause repression. | 7, 44, 53, 55, 60, 103, 115, 147, 151, 166, 167, 184, 210, 251 |
| lamB | 91.5 | Receptor for phage λ and specific pore for maltodextrins (maltoporin, glycoporin). | 16, 39, 85, 92, 124, 136, 207, 231, 263, 265 |
| malM | 91.5 | Periplasmic protein of unknown function, partially associated with the outer membrane. Contains an Ala-Pro linker also found in OmpA. | 104, 222, 234 |
| malP | 76.5 | Maltodextrin phosphorylase. Substrates are maltopentaose and larger maltooligosaccharides. malP mutants still grow on maltose but accumulate large amount of maltodextrins under these conditions. | 177, 181, 229, 242, 290 |
| malQ | 76.4 | Amylomaltase. Maltodextrinyltransferase with maltotriose as the smallest substrate. malQ mutants cannot grow on maltose, are sensitive to maltose, and are constitutive for mal gene expression. | 69, 165, 182, 194, 294, 295 |
| malS | 80.5 | Periplasmic α-amylase, cleaves preferentially maltohexaose from the nonreducing end of meltotextrins. | 91, 92, 235, 256 |
| malZ | 9.1 | Maltodextrin glucosidase and γ-cyclodextrinase, cleaves glucose sequentially from the reducing end of maltodextrins. Maltotriose is the smallest substrate. It linearizes γ-cyclodextrin but not α- and β-cyclodextrin. | 185, 211, 267 |
| Genes whose products control mal gene expression | |||
| cya | 85.9 | Adenylate cyclase. Production of cAMP, involvement in catabolite repression. | 75, 134, 187 |
| crp | 75.1 | cAMP-binding protein, needed for the transcription of malT and the transport gene cluster. | 35, 135, 143, 206 |
| malI | 36.6 | Repressor for malXY, not dependent on MalT, inducer unknown. | 209 |
| malX | 36.6 | Enzyme II of the PTS, transports and phosphorylates glucose, can transport maltose by diffusion. | 208 |
| malY | 36.6 | βC-S lyase (cystathionase). Overproduction reduces mal gene expression by interaction with MalT and its inactivation. | 208, 301 |
| aes (ybaC, orf203) | 10.8 | Esterase. Overproduction reduces mal gene expression, presumably by interaction with MalT and its inactivation. | 164, 186 |
| mlc | 35.9 | Gene regulator, represses the expression of malT and manXYZ. | 70, 131 |
| maa (mac, F183a) | 10.32 | Glucose/maltose transacetylase, not MalT dependent, responsible for exit of maltose and glucose in their acetylated forms. | 20, 26 |
| Genes whose products affect endogenous synthesis of inducer | |||
| glgA | 75.4 | Glycogen synthase. ADP-dependent synthesis of glycogen. Degradation of glycogen yields maltotriose, which, in malQ mutants, leads to constitutivity of the maltose system. glgA mutants have a lower level on uninduced mal gene expression than glgA+ strains. | 148, 176 |
| glgC | 75.4 | ADP-glucose-pyrophosphorylase. Synthesis of ADP-glucose, needed for constitutive mal gene expression in malQ mutants. glgC mutants have a lower uninduced mal gene expression than glgC+ strains. | 4, 176 |
| glgP | 75.4 | Glycogen phosphorylase. Glycogen degradation and formation of glucose-1-phosphate. Possibly involved in synthesis of endogenous inducer. | 300 |
| glgB | 75.4 | Branching enzyme | 5, 176 |
| glgX | 75.4 | Amylase-like enzyme, role in glycogen degradation unclear. | 221 |
| amyA | 43.2 | Cytoplasmic α-amylase, not MalT dependent, no apparent role in glycogen degradation. | 198 |
| galU | 27.8 | UDP-glucose pyrophosphorylase. Possible origin of cytoplasmic unphosphorylated glucose. | 292 |
| glgS | 68.7 | Short polypeptide, involved in RpoS-dependent glycogen synthesis. | 11, 118 |
| glk | 54.0 | Glucokinase. Reduces level of internal glucose which can form endogenous inducer, responsible for mal gene repression at high osmolarity. | 43, 95, 161 |
| treR | 96.2 | Repressor for treB and treC. treR mutants allow transport of maltose via the treB-encoded transport system and induce treC, whose product is involved in inducer synthesis. | 129 |
| treB | 96.1 | Enzyme II for trehalose of the PTS, allows transport of maltose. | 142 |
| treC | 96.1 | Trehalose-6-phosphate hydrolase, involved in inducer synthesis. | 21 |
| pgm | 15.4 | Phosphoglucomutase. Needed for the synthesis of endogenous inducer. A pgm mutant can still grow on maltose but only in the presence of MalZ. | 1, 69, 153, 220 |
| Genes that affect mal gene expression by an unknown mechanism when mutated | |||
| asuE | 25.6 | tRNA-modifying enzyme. An asuE mutant increases mal gene expression at high osmolarity. | 262 |
| yjeA (genX) | 94.4 | Homolog to lysyl-tRNA synthases LysS and LysU. A genX mutant interferes with the ability of a malQ malZ292 pgm strain to grow on maltose. | 146, 170 |
| envZ | 76.1 | Sensor kinase of the two-component osmoregulatory system. Certain envZ mutants that lead to the overphosphorylation of OmpR show reduced malT expression. | 33 |
| phoP phoQ | 25.7 | Two-component system responding to Mg2+ starvation. Overexpression of the response regulator leads to mal gene repression. | 278, 283 |