A leader open reading frame is essential for the expression in Escherichia coli of GC-rich leuB gene of an extreme thermophile, Thermus thermophilus

Cloning and expression of heterologous genes in Rhodothermus marinus

The construction of a shuttle cloning system for Rhodothermus marinus and Escherichia coli is described. It is based on the shuttle vector pRM3000, which contains a multiple cloning site as well as the shuttle marker trpB and TrpB(-) recipients of both species. The vector is stable and in 25 +/- 2 and 91 +/- 3 copies in R. marinus SB-1 and E. coli SDH-1, respectively. Three different R. marinus regulatory sequences of the dnaJ, dnaK and recA genes were integrated into pRM3000 to make the expression vectors pRM5100, pRM5200 and pRM5300, respectively. Genes encoding alpha- and beta-galactosidase (agaT and bgaT) from Thermus brockianus were cloned in R. marinus. Expression of both recombinant genes in R. marinus was demonstrated. The agaT gene was used as a reporter to study transcription from the expression vectors. Induced expression by ten- and twentyfold was observed from the dnaK and dnaJ regulatory sequences, respectively, after a temperature shift from 63 to 77 degrees C. This is the first report of cloning and expression of heterologous genes in R. marinus and the first study of promoter activity in the species.

Heterologous gene expression in Thermus thermophilus: beta-galactosidase, dibenzothiophene monooxygenase, PNB carboxy esterase, 2-aminobiphenyl-2,3-diol dioxygenase, and chloramphenicol acetyl transferase

Enzymes from thermophiles are preferred for industrial applications because they generally show improved tolerance to temperature, pressure, solvents, and pH as compared with enzymes from mesophiles. However, nearly all thermostable enzymes used in industrial applications or available commercially are produced as recombinant enzymes in mesophiles, typically Escherichia coli. The development of high-temperature bioprocesses, particularly those involving cofactor-requiring enzymes and/or multi-step enzymatic pathways, requires a thermophilic host. The extreme thermophile most amenable to genetic manipulation is Thermus thermophilus, but the study of expression of heterologous genes in T. thermophilus is in its infancy. While several heterologous genes have previously been expressed in T. thermophilus, the data reported here include the first examples of the functional expression of a gene from an archaeal hyperthermophile ( bglA from Pyrococcus woesei), a cofactor-requiring enzyme ( dszC from Rhodococcus erythropolis IGTS8), and a two-component enzyme ( carBa and carBb from Sphingomonas sp. GTIN11). A thermostable derivative of pnbA from Bacillus subtilis was also expressed, further expanding the list of genes from heterologous hosts that have been expressed in T. thermophilus.

Overexpression in Escherichia coli of the AT-rich trpA and trpB genes from the hyperthermophilic archaeon Pyrococcus furiosus

Expression of AT-rich genes from microorganisms such as archaea is often inefficient in Escherichia coli. The trpA and trpB genes encoding the tryptophan synthase subunits were cloned from the hyperthermophilic archaeon Pyrococcus furiosus. No apparent difference in codon bias was found between the genes. However, using a conventional cloning vector having the lac promoter, the trpB gene was expressed poorly in E. coli, whereas the trpA gene was overexpressed. The expression of the trpB gene was remarkably enhanced (>12-fold) by the introduction of an overlapping leader open reading frame. The expression of the trpA gene was also improved ( approximately 1.5-fold). This approach may be useful for overexpressing various kinds of AT-rich genes.

Cloning of the gene encoding a novel thermostable alpha-galactosidase from Thermus brockianus ITI360

An alpha-galactosidase gene from Thermus brockianus ITI360 was cloned, sequenced, and expressed in Escherichia coli, and the recombinant protein was purified. The gene, designated agaT, codes for a 476-residue polypeptide with a calculated molecular mass of 53, 810 Da. The native structure of the recombinant enzyme (AgaT) was estimated to be a tetramer. AgaT displays amino acid sequence similarity to the alpha-galactosidases of Thermotoga neapolitana and Thermotoga maritima and a low-level sequence similarity to alpha-galactosidases of family 36 in the classification of glycosyl hydrolases. The enzyme is thermostable, with a temperature optimum of activity at 93 degrees C with para-nitrophenyl-alpha-galactopyranoside as a substrate. Half-lives of inactivation at 92 and 80 degrees C are 100 min and 17 h, respectively. The pH optimum is between 5.5 and 6.5. The enzyme displayed high affinity for oligomeric substrates. The K(m)s for melibiose and raffinose at 80 degrees C were determined as 4.1 and 11.0 mM, respectively. The alpha-galactosidase gene in T. brockianus ITI360 was inactivated by integrational mutagenesis. Consequently, no alpha-galactosidase activity was detectable in crude extracts of the mutant strain, and it was unable to use melibiose or raffinose as a single carbohydrate source.