Herbivore-Algal relationships on a coastal rock platform (Cape Banks,N.S.W.)

Summary A fifty-three metre inter-tidal transect on a headland near Sydney, New South Wales, has been studied. Its profile, fauna and flora are illustrated and described.Figures were prepared indicating the herbivore standing crop on this transect at various seasons, and some evidence of seasonal changes in the marine algal flora is presented.All macroscopic herbivorous animals were removed from the transect at two-weekly intervals during a twelve month period. After the initiation of this treatment no species of alga in the transect appeared outside the zone in which it normally occurred. There was thus no indication that animal browsing normally restricts algae to particular (vertical) zones on this rock platform. The abundance of certain species was, however, affected by the removal of the herbivores. First to flourish were the green algae; contrary to results obtained in other parts of the world, brown algae did not then become established to form a climax community. It is suggested that the rapid reinvasion by herbivores noted at Cape Banks may account for differences in these results from those recorded elsewhere.Some algal taxonomic notes are appended.     

The formation of vesicles in the developmental cycle of the nodular endophyte of Hippophaë rhamnoides L.

Summary The mature vesicle of the Hippophaë rhamnoides root nodule endophyte is spherical, approximately 3–4 m in diameter and exhibits a high degree of apparently random septation. Electron micrographs are presented which show that this vesicular form in the endophytic development within the host cell originates as a swelling of the hyphal tip. The young vesicle is non-septate and in general attains a minimum diameter of 3 m before septation becomes evident. The number of septa then increases with vesicle maturity.     

A systematic study of the effect of physiological factors on beta2-microglobulin amyloid formation at neutral pH

Beta(2)-microglobulin (beta(2)m) forms amyloid fibrils that deposit in the musculo-skeletal system in patients undergoing long-term hemodialysis. How beta(2)m self-assembles in vivo is not understood, since the monomeric wild-type protein is incapable of forming fibrils in isolation in vitro at neutral pH, while elongation of fibril-seeds made from recombinant protein has only been achieved at low pH or at neutral pH in the presence of detergents or cosolvents. Here we describe a systematic study of the effect of 11 physiologically relevant factors on beta(2)m fibrillogenesis at pH 7.0 without denaturants. By comparing the results obtained for the wild-type protein with those of two variants (DeltaN6 and V37A), the role of protein stability in fibrillogenesis is explored. We show that DeltaN6 forms low yields of amyloid-like fibrils at pH 7.0 in the absence of seeds, suggesting that this species could initiate fibrillogenesis in vivo. By contrast, high yields of amyloid-like fibrils are observed for all proteins when assembly is seeded with fibril-seeds formed from recombinant protein at pH 2.5 stabilized by the addition of heparin, serum amyloid P component (SAP), apolipoprotein E (apoE), uremic serum, or synovial fluid. The results suggest that the conditions within the synovium facilitate fibrillogenesis of beta(2)m and show that different physiological factors may act synergistically to promote fibril formation. By comparing the behavior of wild-type beta(2)m with that of DeltaN6 and V37A, we show that the physiologically relevant factors enhance fibrillogenesis by stabilizing fibril-seeds, thereby allowing fibril extension by rare assembly competent species formed by local unfolding of native monomers.     

Localization and induction of the A2 virulence factor in Leishmania: evidence that A2 is a stress response protein

Leishmaniasis is a vector‐borne infectious disease with a wide range of pathologies depending on the species of Leishmania. Leishmania parasites are transmitted by the sand fly vector as promastigotes; within the mammalian host, Leishmania parasites differentiate into amastigotes and replicate in macrophages. The A2 protein from Leishmania donovani is expressed predominantly in amastigotes and therefore likely plays a role in survival in the mammalian host. In the present study, we have determined that the A2 protein colocalized with the Leishmania endoplasmic reticulum binding protein, BiP, was induced by stress and complexed with BiP following heat shock. The A2 gene in Leishmania major is a non‐expressed pseudogene, and we present evidence that ectopic expression of a transfected A2 gene in L. major enhanced its viability following heat shock. A2 may therefore play a role in protecting L. donovani from stress associated with infection in visceral organs, including the fever typically associated with visceral leishmaniasis. Interestingly, when comparing A2 protein localization, we also observed that the Leishmania secreted acid phosphatase SAcP protein was transported out of the parasite‐containing phagolysosome and was located throughout the macrophage cytoplasm in vesicles, providing the first example of a secreted Leishmania‐derived protein exiting the parasite‐containing phagolysosome.     

Kallikrein-mediated cell signalling: targeting proteinase-activated receptors (PARs)

We tested the hypothesis that human tissue kallikreins (hKs) may regulate signal transduction by cleaving and activating proteinase-activated receptors (PARs). We found that hK5, 6 and 14 cleaved PAR N-terminal peptide sequences representing the cleavage/activation motifs of human PAR1 and PAR2 to yield receptor-activating peptides. hK5, 6 and 14 activated calcium signalling in rat PAR2-expressing (but not background) KNRK cells. Calcium signalling in HEK cells co-expressing human PAR1 and PAR2 was also triggered by hK14 (via PAR1 and PAR2) and hK6 (via PAR2). In isolated rat platelets that do not express PAR1, but signal via PAR4, hK14 also activated PAR-dependent calcium signalling responses and triggered aggregation. The aggregation response elicited by hK14 was in contrast to the lack of aggregation triggered by hK5 and 6. hK14 also caused vasorelaxation in a phenylephrine-preconstricted rat aorta ring assay and triggered oedema in an in vivo model of murine paw inflammation. We propose that, like thrombin and trypsin, the kallikreins must now be considered as important 'hormonal' regulators of tissue function, very likely acting in part via PARs.     

Kinetic analysis of operator binding by the E. coli methionine repressor highlights the role(s) of electrostatic interactions

MetJ is a member of the ribbon-helix-helix class of DNA-binding proteins whose affinity for operators is apparently controlled by an unprecedented long-range electrostatic effect from the tertiary sulphur atom of its co-repressor, S-adenosyl methionine. We report here the results of kinetic assays of DNA binding with MetJ mutant proteins having altered net charges. The results (a) suggest that MetJ locates its operators via a sliding mechanism, (b) support the idea that electrostatic steering is important in the initial DNA binding event and (c) highlight the sensitivity of this system to electrostatic effects.     

Three different pathological lesions in the <Emphasis Type="Italic">NF1</Emphasis> gene originating de novo in a family with neurofibromatosis type 1

Three members of a Portuguese family, who exhibited clinical evidence of neurofibromatosis type 1 (NF1), were found to possess different heritable and pathological mutations in their NF1 genes: a 1.5-Mb deletion spanning the entire NF1 gene, a truncating CGA-->TGA transition in exon 22 (R1241X), and a frameshift mutation in exon 29 (5406insT). All three lesions occurred de novo and are likely to have been generated by different mutational mechanisms. At least two of the mutations occurred on different chromosomal backgrounds. The probability of finding three non-identical NF1 gene lesions arising de novo in a family with NF1 is very remote, too low to be readily accepted as mere coincidence. A number of possible explanations for this unique finding were therefore explored, but none were found to be wholly convincing. This report nevertheless serves as a reminder that it is unwise, even in the case of an autosomal dominant condition, to extrapolate from the detection of a single mutation in a specific individual to assuming an identical molecular genetic aetiology in other clinically affected members of the same family.