Antitumour activities of levans produced by Zymomonas mobilis strains

Levans produced by four Zymomonas mobilis strains showed antitumour activity against sarcoma 180 and Ehrlich carcinoma in Swiss albino mice. Levans from two strains (ZAP and CP4) had the highest effects. NMR analysis showed that the polymers were composed only of fructose units. The results suggested that the antineoplasic effect is associated to the polysaccharide molecular weight and that a particular molecular weight range may be responsible for this effect.     

New high-toxicity mosquitocidal strains of Bacillus sphaericus lacking a 100-kilodalton-toxin gene.

Five new high-toxicity mosquitocidal strains of Bacillus sphaericus were isolated in Singapore. They all belong to phage group 8 and have binary toxin (51.4- plus 41.9-kDa) genes located on the chromosome but lack a 100-kDa-toxin gene. These strains of B. sphaericus constitute a new subgroup, as only two weakly toxic strains in phage group 8 have previously been described and all the known high-toxicity strains have both binary toxin and 100-kDa-toxin genes.     

Variation in the ribosomal internal transcribed spacers (ITS1 and ITS2) among eight taxa of the Mimulus guttatus species complex

The internal transcribed spacer region (ITS1 and ITS2) of the 18S-25S nuclear ribosomal DNA sequence and the intervening 5.8S region were sequenced from three individuals in each of eight taxa of the Mimulus guttatus species complex. Three discrete variants, or "types," of ITS sequences were found, among which 30%-40% of sites differed, compared with 1%-2% within types. Dot plots indicate that these types were not related by conspicuous rearrangements or inversions. More than one ITS type was often found in the same taxon, and two of three ITS types span species boundaries, indicating their presence prior to speciation. These ITS sequences showed essentially no positional homology with the nearest sequenced relative, tomato. In contrast, the 5.8S region was relatively unvaried, with 8 of 162 sites varied in the sample among all eight taxa. The phylogeny inferred by the most common ITS sequence type, rooted by the two other ITS types, agreed with isozymes in showing the distinctness of M. nudatus, M. laciniatus, and M. tilingii from the other five taxa.      

Variation in heat shock proteins within tropical and desert species of poeciliid fishes

The 70-kilodalton heat shock protein (hsp70) family of molecular chaperones, which contains both stress-inducible and normally abundant constitutive members, is highly conserved across distantly related taxa. Analysis of this protein family in individuals from an outbred population of tropical topminnows, Poeciliopsis gracilis, showed that while constitutive hsp70 family members showed no variation in protein isoforms, inducibly synthesized hsp70 was polymorphic. Several species of Poeciliopsis adapted to desert environments exhibited lower levels of inducible hsp70 polymorphism than the tropical species, but constitutive forms were identical to those in P. gracilis, as they were in the confamilial species Gambusia affinis. These differences suggest that inducible and constitutive members of this family are under different evolutionary constraints and may indicate differences in their function within the cell. Also, northern desert species of Poeciliopsis synthesize a subset of the inducible hsp70 isoforms seen in tropical species. This distribution supports the theory that ancestral tropical fish migrated northward and colonized desert streams; the subsequent decrease in variation of inducible hsp70 may have been due to genetic drift or a consequence of adaptation to the desert environment. Higher levels of variability were found when the 30- kilodalton heat shock protein (hsp30) family was analyzed within different strains of two desert species of Poeciliopsis and also in wild-caught individuals of Gambusia affinis. In both cases the distribution of hsp30 isoform diversity was similar to that seen previously with allozyme polymorphisms.      

Regions of DNA sequence homology between an octopine and a nopaline Ti plasmid of Agrobacterium tumefaciens

Summary Despite the fact that pTiC58 and pTiB6S3 functionally, have been shown to date to have only tumorigenicity and phage AP1 exclusion in common, many restriction fragments of the plasmids contain DNA sequences common to both. The bulk of this homologous DNA is concentrated in a few restriction endonuclease fragments and the remainder is organized in short discontinuous regions spread over many fragments. In pTiB6S3 the bulk of the homology is distributed throughout a 29x10⁶ dalton segment comprising 8 Sma I fragments. This region includes those sequences which are transferred to and transcribed in tumorigenic plant cells induced by B6-806 or closely related strains. The pattern of homology within this portion of the plasmid shows a region of low sequence homology (Sma I Fragment 3 b) apparently corresponding to the gene or genes coding for octopine synthesis in the plant tumor cells, surrounded by regions of high sequence homology. The extent of inter-plasmid homology then decreases with increasing distance from fragment 3b. The remainder of the homology is distributed throughout a segment of maximum size 21.5x10⁶ daltons comprising two Sma I fragments and cannot yet be definitely linked with any specific plasmid function.     

Binding of purified Bacillus sphaericus binary toxin and its deletion derivatives to Culex quinquefasciatus gut: elucidation of functional binding domains.

Highly larvicidal strains of Bacillus sphaericus produce a binary toxin composed of 51 and 42 kDa proteins which binds to sharply delineated regions of the gastric caecum and posterior midgut of susceptible larvae of the mosquito Culex quinquefasciatus. To investigate the role of the individual subunits and the organization of functional binding regions within the toxin, plasmids were constructed for the expression in Escherichia coli of the toxin proteins and their NH2- and COOH-terminal deletion derivatives as fusions with glutathione S-transferase (GST). Toxin proteins were purified by affinity chromatography followed by cleavage from the GST carrier with thrombin. The LC50 values for the purified toxin proteins and their deletion derivatives were determined. The binding patterns of fluorescently labelled toxin suggested that the 51 kDa protein is the primary binding component of the toxin and mediates the regional binding and internalization of the 42 kDa protein. Examination of the toxin deletion derivatives revealed that the NH2-terminal region of the 51 kDa protein was required for binding to the larval gut, whilst the COOH-terminal region was responsible for interacting with the 42 kDa protein. Toxicity was strongly correlated with the subsequent internalization of the toxin, probably by endocytosis.     

Interaction of the Bacillus sphaericus mosquito larvicidal proteins

Genes for 51.4- and 41.9-kDa insecticidal proteins of Bacillus sphaericus were separately cloned and expressed in Escherichia coli. Both proteins were required for toxicity. Approximately equal numbers of cells containing the 51.4- and 41.9-kDa proteins produced the greatest toxicity; excess 41.9-kDa protein did not affect toxicity, whereas excess 51.4-kDa protein reduced activity. Larvae were killed when 41.9-kDa protein was fed up to 24 h after the 51.4-kDa protein, but not when the order of feeding was reversed. Radiolabelled toxins bound in approximately equal amounts to the gastric caecum and posterior midgut of Culex quinquefasciatus larvae. Radiolabelled 51.4-kDa protein was rapidly degraded by ca. 12-13 kDa in the larval gut, while 41.9-kDa protein was degraded by 1-2 kDa. Nonreduced toxin extracted from B. sphaericus produced a band on SDS-PAGE of ca. 68-74 kDa that contained both 51.4- and 41.9-kDa proteins based on sequence analysis, and a band of ca. 51 kDa that contained primarily 41.9-kDa protein. Escherichia coli containing 51.4-kDa protein enhanced toxicity of the latter eluted SDS-PAGE band. These proteins may associate very strongly, and trace amounts of 51.4-kDa protein in preparations of 41.9-kDa protein from B. sphaericus may be responsible for the previously reported toxicity of the latter.