MTP' R. capsulatus 86,360 542 (S) a Proteins that have been purified to homogeneity and/or for which a complete or partial gene sequence is known. b Numbers in boldface type are precise molecular weights calculated from the determined or deduced amino acid sequence. Other Mrs are estimates of the monomer molecular weight from denaturing gel electrophoresis. Els for which there is good evidence that the native protein is a homodimer are indicated. c Abbreviations: P, references for purification of the protein; S, references for the complete sequence of the gene or protein; s, references for only a partial sequence; c, molecular weight determined by the size of the product expressed from the cloned gene.

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Glc) and catabolite repression mediated by the global regulator cyclic AMP (cAMP)-cAMP receptor protein (CRP). We measured in a systematic way the relation between cellular growth rates and the key parameters of catabolite repression, i.e., the phosphorylated EIIA Crr (EIIA Crr ϳP) level and the cAMP level, using in vitro and in vivo assays. Different growth rates were obtained by using either various carbon sources or by growing the cells with limited concentrations of glucose, sucrose, and mannitol in continuous bioreactor experiments. The ratio of EIIA Crr to EIIA Crr ϳP and the intracellular cAMP concentrations, deduced from the activity of a cAMP-CRP-dependent promoter, correlated well with specific growth rates between 0.3 h ؊1 and 0.7 h ؊1 , corresponding to generation times of about 138 and 60 min, respectively. Below and above this range, these parameters were increasingly uncoupled from the growth rate, which perhaps indicates an increasing role executed by other global control systems, in particular the stringent-relaxed response system.In Escherichia coli, the phosphoenolpyruvate (PEP)-dependent phosphotransferase systems (PTSs) represent important uptake systems for a number of carbohydrates which mediate transport and concomitant phosphorylation of their respective substrates (10,44). In addition to their transport function, all components of the various PTSs of a cell form an important signal transduction system. The signal transduction properties of the PTS depend on the phosphorylation state of its proteins (26,49). The PTSs usually consist of two general proteins, i.e., the PEP-dependent protein kinase enzyme I (EI), and the histidine-containing protein (HPr), and up to 20 different, substrate-specific enzymes II (EII). EII usually comprise two soluble domains EIIA and EIIB involved in phosphotransfer and the membrane-bound transporter domain EIIC (44). The major regulatory output signal of the PTS depends on the phosphorylation level of EIIA Crr (according to its genetic nomenclature), also designated EIIA Glc due to its function as the EIIA domain for the glucose-specific PTS (9, 23, 52). EIIA Crr inhibits the activity of a number of non-PTS transporters and enzymes (8,32,33,35,36), a process referred to as inducer exclusion. Furthermore, the phosphorylated form of EIIA Crr (EIIA Crr ϳP) activates adenylate cyclase (1, 13, 41, 57), which in turn synthesizes cyclic AMP (cAMP) (59). The indicator molecule or alarmone cAMP is the coactivator of the important global transcription factor CRP (cAMP receptor protein). Together, they regulate in a process called cAMP-CRP-dependent catabolite repression efficient transcription of different genes involved in the synthesis of a large number of catabolic enzymes (4,39,43). The central role of EIIA Crr ϳP in the activation of adenylate cyclase is largely based on mutant analysis (13,23,33).The phosphorylation state of the PTS and hence the intracellular cAMP concentrations are postulated to depend largely on two major factors: (i) the uptake rate of any P...

Numerous gram-negative and gram-positive bacteria take up carbohydrates through the phosphoenolpyruvate (PEP):carbohydrate phosphotransferase system (PTS). This system transports and phosphorylates carbohydrates at the expense of PEP and is the subject of this review. The PTS consists of two general proteins, enzyme I and HPr, and a number of carbohydrate-specific enzymes, the enzymes II. PTS proteins are phosphoproteins in which the phospho group is attached to either a histidine residue or, in a number of cases, a cysteine residue. After phosphorylation of enzyme I by PEP, the phospho group is transferred to HPr. The enzymes II are required for the transport of the carbohydrates across the membrane and the transfer of the phospho group from phospho-HPr to the carbohydrates. Biochemical, structural, and molecular genetic studies have shown that the various enzymes II have the same basic structure. Each enzyme II consists of domains for specific functions, e.g., binding of the carbohydrate or phosphorylation. Each enzyme II complex can consist of one to four different polypeptides. The enzymes II can be placed into at least four classes on the basis of sequence similarity. The genetics of the PTS is complex, and the expression of PTS proteins is intricately regulated because of the central roles of these proteins in nutrient acquisition. In addition to classical induction-repression mechanisms involving repressor and activator proteins, other types of regulation, such as antitermination, have been observed in some PTSs. Apart from their role in carbohydrate transport, PTS proteins are involved in chemotaxis toward PTS carbohydrates. Furthermore, the IIAGlc protein, part of the glucose-specific PTS, is a central regulatory protein which in its nonphosphorylated form can bind to and inhibit several non-PTS uptake systems and thus prevent entry of inducers. In its phosphorylated form, P-IIAGlc is involved in the activation of adenylate cyclase and thus in the regulation of gene expression. By sensing the presence of PTS carbohydrates in the medium and adjusting the phosphorylation state of IIAGlc, cells can adapt quickly to changing conditions in the environment. In gram-positive bacteria, it has been demonstrated that HPr can be phosphorylated by ATP on a serine residue and this modification may perform a regulatory function.

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