Eight mutants of Alcaligenes eutrophus defective in the intracellular accumulation of poly-fi-hydroxybutyric acid (PHB) were isolated after transposon TnS mutagenesis with the suicide vector pSUP5011. EcoRI fragments which harbor TnS-mob were isolated from pHC79 cosmid gene banks. One of them, PPT1, was used as a probe to detect the intact 12.5-kilobase-pair EcoRI fragment PP1 in a XL47 gene bank ofA. eutrophus genomic DNA. In six of these mutants (PSI, API, GPI, GPIV, GPV, and GPVI) the insertion of TnS-mob was physically mapped within a region of approximately 1.2 kilobase pairs in PP1; in mutant API, cointegration of vector DNA has occurred. In two other mutants (GPII and GPIII), most probably only the insertion element had inserted into PP1. All PHB-negative mutants were completely impaired in the formation of active PHB synthase, which was measured by a radiometric assay. In addition, activities of f-ketothiolase and of NADPH-dependent acetoacetyl coenzyme A (acetoacetyl-CoA) reductase were diminished, whereas the activity of NADH-dependent acetoacetyl-CoA reductase was unaffected. In all PHB-negative mutants the ability to accumulate PHB was restored upon complementation in trans with PP1. The PHB-synthetic pathway of A. eutrophus was heterologously expressed in Escherichia coli. Recombinant strains of E. coli JM83 and K-12, which harbor pUC9-1::PP1, pSUP202::PP1, or pVK101::PP1, accumulated PHB up to 30% of the cellular dry weight. Crude extracts of these cells had significant activities of the enzymes PHB synthase, f-ketothiolase, and NADPH-dependent acetoacetyl-CoA reductase. Therefore, PP1 most probably encodes all three genes of the PHB-synthetic pathway in A. eutrophus. In addition to PHB-negative mutants, we isolated mutants which accumulate PHB at a much lower rate than the wild type does. These PHB-leaky mutants exhibited activities of all three PHB-synthetic enzymes; TnS-mob had not inserted into PP1, and the phenotype of the wild type could not be restored with fragment PP1. The rationale for this mutant type remains unknown.

Tumours ferment glucose to lactate even in the presence of oxygen (aerobic glycolysis; Warburg effect). The pentose phosphate pathway (PPP) allows glucose conversion to ribose for nucleic acid synthesis and glucose degradation to lactate. The nonoxidative part of the PPP is controlled by transketolase enzyme reactions. We have detected upregulation of a mutated transketolase transcript (TKTL1) in human malignancies, whereas transketolase (TKT) and transketolase-like-2 (TKTL2) transcripts were not upregulated. Strong TKTL1 protein expression was correlated to invasive colon and urothelial tumours and to poor patients outcome. TKTL1 encodes a transketolase with unusual enzymatic properties, which are likely to be caused by the internal deletion of conserved residues. We propose that TKTL1 upregulation in tumours leads to enhanced, oxygen-independent glucose usage and a lactatebased matrix degradation. As inhibition of transketolase enzyme reactions suppresses tumour growth and metastasis, TKTL1 could be the relevant target for novel anti-transketolase cancer therapies. We suggest an individualised cancer therapy based on the determination of metabolic changes in tumours that might enable the targeted inhibition of invasion and metastasis.

Protein synthesis is the most expensive process in fast-growing bacteria. Experimentally observed growth rate dependencies of the translation machinery form the basis of powerful phenomenological growth laws; however, a quantitative theory on the basis of biochemical and biophysical constraints is lacking. Here, we show that the growth rate-dependence of the concentrations of ribosomes, tRNAs, mRNA, and elongation factors observed in Escherichia coli can be predicted accurately from a minimization of cellular costs in a mechanistic model of protein translation. The model is constrained only by the physicochemical properties of the molecules and has no adjustable parameters. The costs of individual components (made of protein and RNA parts) can be approximated through molecular masses, which correlate strongly with alternative cost measures such as the molecules’ carbon content or the requirement of energy or enzymes for their biosynthesis. Analogous cost minimization approaches may facilitate similar quantitative insights also for other cellular subsystems.

(TTGACA-18N-AACAAT), exhibiting striking homology to the Escherichia coli WJ70 promoter consensus sequence, was identified approximately 310 bp 5' upstream from the translation initiation codon. An Si nuclease protection assay mapped the transcription start point of phbC 6 bp downstream from this promoter. The location of the promoter was confirmed by analyzing the expression of active PHB synthase in clones of E. coli harboring 5' upstream deletions of phbC ligated to the promoter of the lacZ gene (lacZp) in a Bluescript vector. Plasmids dol81 and do218, which were deleted for the first 108 or 300 bp of the phbC structural gene, respectively, conferred the ability to synthesize large amounts of different truncated PHB synthase proteins to the cells. These proteins contributed to approximately 10% of the total cellular protein as estimated from sodium dodecyl sulfate-polyacrylamide gels. The modified PHB synthase encoded by plasmid dol81 was still active. Clones in which the lacZp-'phbC fusion harbored the complete phbC structural gene plus the phbC ribosome binding site did not overexpress PHB synthase.In Alcaligenes eutrophus, synthesis of poly(3-hydroxybutyric acid) (PHB) starts from acetyl coenzyme A (acetylCoA) and is accomplished by three enzymatic reactions: (i) condensation of two acetyl-CoA units to acetoacetyl-CoA, (ii) chiral reduction of acetoacetyl-CoA to D-(-)-3-hydroxybutyryl-CoA, and (iii) polymerization of D-(-)-3-hydroxybutyrate units. The A. eutrophus PHB-biosynthetic genes phbA (for 3-ketothiolase), phbB (NADPH-dependent acetoacetyl-CoA reductase), and phbC (PHB synthase) have been cloned recently (40, 42). The genes are clustered and are presumably organized in one operon. The genes were expressed in Escherichia coli and in different species of the genus Pseudomonas belonging to rRNA homology group I; they conferred the ability to accumulate polyesters consisting of 3-hydroxybutyrate on most of the recombinant cells (40,(42)(43)(44)(45).Subcloning experiments (28, 29, 41, 42), analysis of transposon TnS-induced PHB-negative mutants (40,41), and nucleotide sequence data (28, 29; this study) provided evidence that the three genes are organized in one operon (phbC-phbA-phbB). It turned out that the sequence data obtained in our and in Dr. Sinskey's laboratory were almost identical. We hesitated to publish this sequence because the N-terminal amino acid sequence of the PHB synthase protein was not known at that time and the promoter of phbC had not been mapped. Although the nucleotide sequence of an open reading frame for phbC was published recently, the transcription and translational initiation sites were not mapped (29). Furthermore, the molecular mass of the gene * Corresponding author. product most likely representing PHB synthase protein obtained in maxicell experiments was only 58,000 Da, whereas the molecular mass of PHB synthase predicted from the amino acid sequence deduced from the putative open reading frame was 63,940 Da (29). This indicated that other translational initiation codon...

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