Replication of pKYM requires the plasmid-encoded RepK protein, which specifically binds to the replication origin of the plasmid. This binding was easily detected in a gel-shift assay. We have used this characteristic to purify RepK protein, to near homogeneity. The repK gene was placed under the control of the phage T7 RNA polymerase promoter on a plasmid. Upon induction of T7 RNA polymerase, Escherichia coli clones containing the recombinant plasmid overproduced the RepK protein, which was then purified in significant quantities. The molecular weight of the RepK protein under denaturing conditions is 36, 000, which is consistent with the size predicted from the DNA sequence data. The N-terminal amino acid sequence determined for the purified RepK matches that deduced from the DNA sequence. RepK protein appears to bind to the replication origin as a monomer with a dissociation constant (Kd) of 2.7×10-9M.
The replication origin of plasmid pKYM, which replicates via a rolling-circle mechanism, is composed of three regions with the following characteristics. 1) The core origin, which is essential for initiation of DNA replication, consists of 39-base pairs. The purified Rep protein of pKYM (RepK) binds specifically to this 39-base-pair region. Within the 39 base-pair origin, there is a sequence of 22 base pairs that is sufficient for termination. 2) The initiation-enhancing region consists of a 98-base-pair-region downstream of the core origin. A host protein(s) binds to this region in the presence of RepK. 3) A 34-base-pair sequence upstream of the core origin is essential for the multiplication of pKYM. Multimers of the plasmid DNA were produced in the absence of this region. The region may enhance correct processing of the unit length plasmid DNA. A host protein binds to this region.
Two mutants of Zymomonas mobilis defective in phosphatidylethanolamine N-methyltransferase have been isolated. One mutant was completely defective in all of the three N-methyltransferase activities dependent on phosphatidylethanolamine, phosphatidyl-N-monomethylethanolamine and phosphatidyl-N, N-dimethylethanolamine, respectively. The other was a leaky mutant in which the three enzyme activities were all equally reduced to 3.4-6.7% of those in the parent strain. Two revertants were derived from the leaky mutant, and in both all three enzyme activities were restored to nearly the same levels as those in the wild-type strain.
The causative agents of trichosporonosis, Trichosporon cutaneum and its synonyms, were reclassified on the basis of DNA relatedness and the coenzyme Q system. Of the 21 strains, 13 have the Q9 system and could be divided into 5 species with 5 varieties, and 8 have Q10, divided into 4 species. Five intermediate DNA relatedness values were found, as the varietal level, in the Q9 group. Taxonomic relationships among strains showing intermediate values were determined from the results obtained by 2 different methods, the spectrophotometric method and the chemiluminometric method. Based on this study, the following new combinations have been described. These are: Trichosporon loubieri (Morenz) Weijman var. laibachii (Windisch) Shinoda et Sugita, comb. nov., T. asahii Akagi var. faecalis (Batista et Silveira) Shinoda et Sugita, comb. nov., and T. asahii var. coremiformis (Moore) Shinoda et Sugita, comb. nov.
A bacteriocidal effect of 2-deoxy-D-galactose (dGal) in addition to the well known static effect was newly demonstrated on the basis of various physiological and biochemical events in Escherichia coli. Unlike D- galactose-induced lysis of a E. coli galE mutant via the process of uridine 5′-diphosphate galactose accumulation, dGal-induced growth inhibition was characterized by cell burst without swelling and elongation of the original rod shaped cells. 2-Deoxy-D-galactose 1-phosphate (dGal1P) was the most probable effector for a bacteriocidal effect of dGal owing to the relationship between dGal-sensitive phenotype and plasmid-dependent galK gene expression. The synthesis of cell wall polysaccharides was functional in dGal-grown cells with the added D-glucosamine and N-acetyl-D-glucosamine, which were protective against dGal-induced growth inhibition. The present study proposes inhibition of fructose 1, 6- bisphosphatase related to de novo synthesis of amino sugar with accumulation of dGal1P as a cause of overall growth inhibition by dGal.
Initial reduction of the boundaries of the Xanthomonas albilineans (XAI-I) β-endoglucanase (egxA) gene encoded on a 7.1-kb DNA fragment resulted in the isolation of a 2.0-kb fragment encoding activity. Nucleotide sequence determination and analysis revealed an open reading frame (ORF) for the egxA gene starting at position 521bp, extending for 1, 086bp and coding for a 361-amino acid (aa) protein. Upstream of the egxA ORF, an additional ORF (ORF-2) and two Escherichia coli-like promoters (P1 and P2) were identified. The two promoter sequences were found to operate independently. Removal of P1 and most of ORF-2 appeared to result in increased expression of egxA. Analysis of the deduced egxA as sequence revealed features common amongst known endoglucanases, including a proline-threonine-serine as region and a signal peptide with a predicted cleavage site after alanine27. The protein displayed some degree of homology to members of the cellulase A family.
The objective of this study was to isolate and characterize thermostable microbial lipases. An enrichment culture technique was used to enrich for thermophiles capable of utilizing olive oil as a carbon source. Out of 44 initial isolates, strain H1, which exhibits the highest lipase activity, was chosen for further characterization. Strain H1 was a spore forming rod, capable of growing at 65°C and was assigned as a Bacillus sp. Optimal lipase production was on medium containing 1% Tween 80. Lipase H1 was partially purified by acetone precipitation, anion exchange chromatography and gel filtration. The enzyme has a molecular weight of 20, 000 (based on gel filtration) and is most active at pH 7.0 at 70°C with a half-life of 50h at 60°C. Lipase H1 had no apparent requirement for cofactors and its activity was completely inhibited in the presence of 1mM HgCl2. The best substrates for the enzyme were short-chain fatty acid esters. With β-naphthyl caprylate as a substrate, the enzyme has a Km of 0.02mM.
Low density (LDPE) and high density (HDPE) polyethylene films filled with starch up to a maximum level of 20% by weight were tested for biodegradation under different environmental conditions. Composting windrows consisting of various putrescible waste and assembled for controlled biostabilization management under static conditions were used. The physical and chemical deterioration of the polyethylene-starch films exposed to a controlled composting environment were recorded and analyzed with respect to the different composting evolution and were compared with the data collected in pure culture systems and in bench scale tests simulating an aerobic biostabilization process. Evidences are presented on the partial removal of starch from the different films as a consequence of massive surface colonization by various microorganisms. Loss of starch is accompanied by a small but significant drop in the average molecular weight and decrement in mechanical strength. In the case of a composting trial experiencing prolonged severe temperature conditions, a small but spectroscopically detectable oxidation of the polyethylene matrix was also observed. Efficiency of the controlled composting systems can be claimed in assessing reproducible conditions in an accelerated biostabilization of putrescible matter and hence versatility in the evaluation of the degradation of plastic manufacts.