Biomedical subjects
Publications and source records attributed to B Diderichsen.
A gene encoding an alkaline protease was cloned from an alkalophilic bacillus, and its nucleotide sequence was determined. The cloned gene was used to increase the copy number of the protease gene on the chromosome by an improved gene amplification technique.
We have developed a strategy for the integration and stable amplification of DNA sequences in the chromosome of poorly transformable bacilli, which avoids the presence of a functional plasmid replication system in the integrated DNA. The parental vector for integration contains two plus origins of replication from pUB110 in the same orientation on a single plasmid. Due to the direct repeats, such plasmids produce two individual progeny vectors, one of which is dependent on the other for replication, as it lacks a functional rep gene. We have used such a progeny vector system to integrate and amplify DNA on the chromosome of Bacillus licheniformis, and show that the structure is stable in the absence of selective pressure.
The lipA gene of Pseudomonas cepacia DSM3959 requires a downstream gene, limA, in oder to express lipase activity. The product of the lim gene, LimA, is a molecular chaperone required during the folding of lipase in oder for the lipase to adopt an active conformation. The lipase and LimA proteins have been shown to form a complex precipitable with either an anti-lipase or anti-LimA antibody. LimA has been shown to form a 1:1 complex with with prelipase and lipase isolated from "natural" P. cepacia system. The mature lipase (lacking its signal peptide) has been expressed in the presence and absence of LimA in Escherichia coli. LimA can activate mature lipase during a urea denaturation-renaturation experiment, indicating that the signal peptide is not required for the lipase to be activated by LimA. The effects of various reagents on the renaturation of lipase from 8 M urea have been examined. We propose a mechanism for the function of the LimA chaperone during the production of active extracellular lipase.
A deletion of the spoIIAC gene of Bacillus licheniformis was prepared in vitro by using the splicing-by-overlap-extension technique. This gene was introduced into B. licheniformis on a temperature-sensitive plasmid, and following integration and excision from the chromosome, a precisely located deletion on the chromosomal gene was prepared. The mutated bacterium was totally asporogenous and formed abortively disporic cells characterized by asymmetric septa at the poles of the cells. Qualitative plate tests revealed that the bacterium synthesized normal levels of DNase, polygalacturonate lyase, protease, RNase, and xylanase, but the hydrolysis zones due to beta-1,3-glucanase and carboxymethyl cellulase activity were smaller in the mutant than in the parent strain. The synthesis of alkaline protease was the same in batch cultures of the mutant and the parent during prolonged incubation for 72 h, but the alpha-amylase yields were reduced by about 30% by the mutation.
An extracellular Pseudomonas cepacia lipase, LipA, is inactive when expressed in the absence of the product of the limA gene. Evidence has been presented that LimA is a molecular chaperone. The lipA and limA genes have been cloned in separate and independently inducible expression systems in Escherichia coli. These systems were used to test the molecular chaperone hypothesis by investigating whether LimA could activate presynthesized prelipase and whether presynthesized LimA could activate newly synthesized prelipase. The results show that LimA cannot activate presynthesized prelipase and that presynthesized LimA can activate only a limited number of de novo synthesized prelipase molecules. Co-immunoprecipitation of prelipase/lipase with LimA generated a 1:1 complex of prelipase/lipase and LimA. The results suggest that a 1:1 complex of LipA and LimA is required for prelipase processing and secretion of active lipase.
A fragment from Bacillus acidopullulyticus strain 294-16 encoding a pullulanase activity has been cloned into Bacillus subtilis. The nucleotide sequence of the 3972 base pairs (bp) fragment has been determined and shown to include only one complete open reading frame (ORF) of 863 codons. The deduced amino acid sequence of this ORF, denoted pulB, shows homology to a number of amylolytic enzymes. Primary and secondary structure analysis indicates that the central region of the protein forms the catalytic domain in a characteristic (beta/alpha)8 barrel. Three carboxylic acid residues essential for catalysis were identified. Regions within the catalytic domain proposed to be involved in substrate binding have been identified by homology.
The gene lipA of Pseudomonas cepacia DSM 3959 encodes a prelipase from which a signal peptide is cleaved during secretion, producing a mature extracellular lipase. Expression of lipase in several heterologous hosts depends on the presence of another gene, limA, in cis or in trans. Lipase protein has been overproduced in Escherichia coli in the presence and absence of the lipase modulator gene limA. Therefore, limA is not required for the transcription of lipA or for the translation of the lipA mRNA. However, no lipase activity is observed in the absence of limA. limA has been overexpressed and encodes a 33-kDa protein, Lim. If lipase protein is denatured in 8 M urea and the urea is removed by dialysis, lipase activity is quantitatively recovered provided Lim protein is present during renaturation. Lip and Lim proteins form a complex precipitable either by an anti-lipase or anti-Lim antibody. The Lim protein has therefore the properties of a chaperone.
We have constructed plasmid pDN1050, a new small cloning vector for Bacillus subtilis. pDN1050 harbors the origin of replication of Staphylococcus aureus plasmid pUB110 and the chloramphenicol resistance gene of S. aureus plasmid pC194. The plasmid is segregationally and structurally stable. Plasmid pDN1370, a low copy number mutant of pDN1050 was isolated and shown to harbor a mutation in the repA gene of the replication protein.
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celA from the cellulolytic bacterium Bacillus lautus PL236 encodes EG-A, an endo-beta-1,4-glucanase. An open reading frame of 2,100 bp preceded by a ribosome-binding site encodes a protein with a molecular mass of 76,863 Da with a typical signal sequence. The NH2-terminal active domain of EG-A is not homologous to any reported cellulase or xylanase and may represent a new family of such enzymes. A 150-amino-acid COOH-terminal peptide is homologous to noncatalytic domains in several other cellulases (A. Meinke, N.R. Gilkes, D.G. Kilburn, R.C. Miller, Jr., and R.A.J. Warren, J. Bacteriol. 173:7126-7135, 1991). Upstream of celA, a partial open reading frame encodes a 145-amino-acid peptide which also belongs to the family mentioned. Zymogram analysis of extracts from Escherichia coli and supernatants of Bacillus subtilis and B. megaterium, including protease-deficient mutants thereof, which express celA, revealed two active proteins, EG-A-L and EG-A-S, with Mrs of 74,000 and 57,000, respectively. The proportion of EG-A-L to EG-A-S depends on the extracellular proteolytic activity of the host organism, indicating that EG-A-S arises from posttranslational proteolytic modification of EG-A-L. Since EG-A-S has an NH2 terminus corresponding to the predicted NH2-terminal sequence of EG-A, processing appears to take place between the catalytic and noncatalytic domains described. EG-A-L and EG-A-S were purified to homogeneity and shown to have almost identical characteristics with respect to activity against soluble substrates and pH and temperature dependency. EG-A-L binds strongly to cellulose, in contrast to EG-A-S, and has higher activity against insoluble substrates than the latter. We conclude that the COOH-terminal 17,000-Mr peptide of EG-A-L constitutes a cellulose-binding domain.
We have cloned and sequenced a gene for a heat-stable alpha-amylase from a natural isolate of Bacillus stearothermophilus. Previously, it had been shown that B. stearothermophilus amylase genes may be harboured on indigenous plasmids. We have found that our isolate harbours the amylase gene only on the chromosome and not on its indigenous plasmid.
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The lipA gene encoding an extracellular lipase from Pseudomonas cepacia was cloned and sequenced. Downstream from the lipase gene an open reading frame was identified, and the corresponding gene was named limA. lipA was well expressed only in the presence of limA. limA exerts its effect both in cis and in trans and therefore produces a diffusible gene product, presumably a protein of 344 amino acids. Replacement of the lipA expression signals (promoter, ribosome-binding site, and signal peptide-coding sequences) by heterologous signals from gram-positive bacteria still resulted in limA-dependent lipA expression in Escherichia coli, Bacillus subtilis, and Streptomyces lividans.
This paper describes a novel method for creating exact DNA fusions between any two points in a plasmid carried in Bacillus subtilis. It exploits the homologous in vivo recombination between directly repeated sequences that can be established by insertion of a synthetic oligodeoxyribonucleotide. The method was used to enhance the productivity in B. subtilis of a cloned alpha-amylase (Amy)-encoding gene originating from Bacillus stearothermophilus. Thus, an exact fusion between nucleotide sequences encoding the expression signals, including the signal peptide, of a Bacillus licheniformis Amy-encoding gene and the mature Amy of B. stearothermophilus, was created. The resulting hybrid translational product was processed correctly in B. subtilis during secretion, giving rise to an Amy identical to the mature Amy secreted by B. stearothermophilus.
A gene for alpha-acetolactate decarboxylase (ALDC) was cloned from Bacillus brevis in Escherichia coli and in Bacillus subtilis. The 1.3-kilobase-pair nucleotide sequence of the gene, aldB, encoding ALDC and its flanking regions was determined. An open reading frame of 285 amino acids included a typical N-terminal signal peptide of 24 or 27 amino acids. A B. subtilis strain harboring the aldB gene on a recombinant plasmid processed and secreted ALDC. In contrast, a similar enzyme from Enterobacter aerogenes is intracellular.
Escherichia coli relB mutants react to amino acid starvation by several abnormal responses, including accumulation of a translational inhibitor. We have isolated a relB-complementing plasmid from the Clarke and Carbon E. coli DNA library. From this plasmid we sequenced a 2140-bp segment which included the relB gene by the following two criteria: (i) it complements chromosomal relB mutations, (ii) the corresponding DNA segment cloned from chromosomal DNA of three relB mutants was defective in relB complementation. All three mutations fell within an open reading frame of 79 amino acids. A polypeptide of 9 kd compatible with this open reading frame was synthesized in maxicells and is in all probability the product of the relB gene. By nuclease S1 mapping we have determined the transcription start and stop of an 870 base transcript of the relB gene.
Tn5 transposons were integrated near relB at 34.2 min. ksgB was mapped at 36.4 min, 2 min from its previously assumed position.
A tyrosyl-tRNA synthetase mutant of Escherichia coli was isolated and the tyrS gene assigned a map position between man and pdxH at 36.0 min on the chromosome. The tyrS mutant grew badly on broth as did previously described tyrS mutants. This sensitivity to broth was suppressed by tyrR mutations. F-prime factors were found to complement the tyrS mutation.