Expression of a novel cardiac-specific tropomyosin isoform in humans

Tropomyosins are a family of actin binding proteins encoded by a group of highly conserved genes. Humans have four tropomyosin-encoding genes: TPM1, TPM2, TPM3, and TPM4, each of which is known to generate multiple isoforms by alternative splicing, promoters, and 3' end processing. TPM1 is the most versatile and encodes a variety of tissue specific isoforms. The TPM1 isoform specific to striated muscle, designated TPM1alpha, consists of 10 exons: 1a, 2b, 3, 4, 5, 6b, 7, 8, and 9a/b. In this study, using RT-PCR with adult and fetal human RNAs, we present evidence for the expression of a novel isoform of the TPM1 gene that is specifically expressed in cardiac tissues. The new isoform is designated TPM1kappa and contains exon 2a instead of 2b. Ectopic expression of human GFP.TPM1kappa fusion protein can promote myofibrillogenesis in cardiac mutant axolotl hearts that are lacking in tropomyosin.     

Localized induction of a generalized response against multiple biotic agents in Caribbean sea fans

Although inducible defenses are an important component of the defense systems of a range of modular organisms, little is known about inducible defenses of octocorals. A localized inducible response against multiple enemies was detected in the Caribbean sea fans Gorgonia ventalina L. and G. flabellum L. Field surveys showed that localized purpling, resulting from an increase in the proportion of purple sclerites, was associated with overgrowth by Millepora alcicornis and macroalgae, and infection by the fungus Aspergillus sydowii. To confirm inducibility and to assess specificity of the response, a range of treatments—abrasion, cable tie, M. alcicornis, sea fan tissue infected with A. sydowii (diseased allografts), and healthy allografts—was applied to healthy sea fans. After 10 days, all biotic treatments induced a localized physical response consisting of changes in concentration, type, and color of sclerites; however, antifungal activity of non-polar chemical extracts was unaffected. The purpling response appears to be specific to biotic agents and reduces tissue damage in subsequent interactions.Communicated by H. Lasker     

Sequence specificity of pausing by DNA polymerases

We have constructed recombinant M13 DNA templates containing stretches of oligo (purines) and oligo (pyrimidines). Each of these inserts hinders the advancement of the large fragment of E. coli Pol I during DNA synthesis. The pattern of blockage is independent of changes in KCl or Mg2+ concentrations and pausing is moderately alleviated at lower pH. Blockage is not affected by either the concentration of template or by the position of the DNA primer. The pattern of pause sites is similar for calf thymus DNA polymerase-alpha, implying that replicative barriers are determined by the structure of the DNA at its growing point. There is a lack of correlation between the position of pause sites with different inserts and known alternate DNA structures. Thus, the homo-oligomeric inserts may possess a different structure when complexed with DNA polymerase. This concept accounts for the appearance of unique new upstream and downstream pause sites that result from the insertion of each oligonucleotide.     

Cellulases ofVibrio agar-liquefaciens isolated from sea mud

Vibrio agar-liquefaciens produced the component enzymes of a cellulase complex (exoglucanase, endoglucanase and -glucosidase). Whilst complete cellulase activity occurred in three media, each containing carboxymethylcellulose as the sole carbon source, different activities of the individual enzymes resulted. The enzymes showed a temporal sequence in their activity and differed in pH and temperature optima. NaCl enhanced the enzyme activities to varying degrees at different substrate concentrations.     

The sequence of a peptide containing the active site phosphohistidine residue of phosphoglycerate mutase from chicken breast muscle.

Phosphoglycerate mutase is phosphorylated on a histidine residue by the cofactor of the reaction, 2,3-bisphosphoglycerate (Rose, Z. B. (1970) Arch. Biochem. Biophys. 140, 508-513). The phosphoryl group is readily transferred to the normal acceptors, 3-phosphoglycerate and 2-phosphoglycerate, or to water in the presence of glycolate-2-P. An acid-labile phosphorylated decapeptide has been purified from a tryptic digest of the phosphoenzyme. The amino acid sequence of the peptide has been determined to be: Aal-Gly-Gln-Leu-Asp-Glu-Ser-His-Arg. This sequence bears a striking analogy to part of a highly conserved region of lactate dehydrogenase (residues 100 to 109) (Taylor, S. S., Oxley, S. S., Allison, W. S., and Kaplan, N. O. (1973) Proc. Natl. Acad. Sci. U. S. A. 70, 1970-1974). Evidence from x-ray crystallographic studies indicates that the two enzymes are similar in tertiary structure (Campbell, J. W., Watson, H. C. and Hodgson, G. I. (1974) Nature 250, 301-303).     

The influence of mistletoes on the litter-layer arthropod abundance and diversity in a semi-arid savanna,Southwest Zimbabwe

Aims

The below-canopy soil moisture content and litter-layer arthropod abundance and diversity of Acacia karroo trees parasitized by each of three mistletoe species (Erianthemum ngamicum, Plicosepalus kalachariensis, and Viscum verrucosum) and uninfected A. karroo trees were investigated in semi-arid savanna, southwest Zimbabwe.

Results

The soils below the canopies of mistletoe-infected trees were significantly low in moisture content compared to those beneath uninfected A. karroo trees. Nevertheless, arthropod species diversity was greater by up to 34 % below the canopies of mistletoe-infected trees than beneath uninfected A. karroo trees, with greater abundances beneath trees infected by E. ngamicum and P. kalachariensis. In addition, the majority of the arthropod species associated with mistletoe-infected trees had litter as their dominant foraging substrate.

Conclusions

Our findings show that mistletoes increase the abundance and diversity of litter-dwelling and –foraging arthropods due to increase in the quality and quantity of litterfall beneath mistletoe-infected trees. By altering the below-canopy arthropod communities and soil moisture content, mistletoes have potential to modify ecosystem processes such as decomposition, soil process rates, and nutrient cycling. Therefore, we suggest that the resulting increase in resource heterogeneity plays an important role in determining the structure and functioning of semi-arid savanna ecosystems.     

Genetic diversity in Pareuchaetes insulata and its implications for biological control of Chromolaena odorata

Chromolaena odorata (L.) King & H.E. Robins. (Asteraceae) threatens several economic and environmental activities in the eastern subtropical regions of South Africa and is a target for biological control. Three populations of Pareuchaetes insulata (Walker) (Lepidoptera: Erebidae) originating from Florida (USA), Cuba and Jamaica were released at 30 separate sites in KwaZulu-Natal, South Africa. Subsequent overlapping of two of these populations in the field and the likelihood of interbreeding posed a potential risk of establishment failure. To explore the genetic diversity of the different P. insulata populations and test for the existence of pre- and post-zygotic reproductive isolation between them, molecular analyses and cross-mating experiments were conducted. Mitochondrial DNA sequences revealed significant genetic similarity between them. Cross-mating trials between Floridian and Jamaican populations of P. insulata revealed no significant pre- and post-zygotic isolation, with no demonstrable differences in measured parameters between the ‘parental’ populations, the F₁ ‘hybrids’ and the backcrosses. These results suggest that P. insulata populations released in South Africa are part of the same ‘parental’ population. Genetic incompatibility is, therefore, relatively unlikely to be the cause of any failure in establishment of P. insulata at any of the release sites.