Comparison of sequences from the malB regions of Salmonella typhimurium and Enterobacter aerogenes with Escherichia coli K12: A potential new regulatory site in the interoperonic region

Summary The malE and malK genes from Salmonella typhimurium, and the MalEFG operon and a portion of malK from Enterobacter aerogenes were cloned and sequenced. Plasmid-borne malE genes from both species and the malF and malG genes from E. aerogenes were expressed normally in Escherichia coli, and their products function in maltose transport. This shows that the malB products from the three species are interchangeable, at least in the combinations tested. The general genetic organization of the malB region is conserved. Potential binding sites and distances between them are highly conserved in the regulatory intervals. An unexpected conserved region was detected, which we call the U box, and which could be another target for a regulatory protein. This hypothesis is supported by the presence of the U box in the regulatory, region of the pulA-malX operon in Klebsiella pneumoniae. The intergenic region between malE and malF from S. typhimurium and E. aerogenes, contains inverted repeats similar to the palindromic units (PU or REP) found at the same location in E. coli. The predicted amino acid sequence of the encoded proteins showed 90% or more identity in every pairwise comparison of species.     

Gene sequence for the 9 kDa component of Photosystem II from the cyanobacterium Phormidium laminosum indicates similarities between cyanobacterial and other leader sequences

Summary A 9 kDa polypeptide which is loosely attached to the inner surface of the thylakoid membrane and is important for the oxygen-evolving activity of Photosystem II in the thermophilic cyanobacterium Phormidium laminosum has been purified, a partial amino acid sequence obtained and its gene cloned and sequenced. The derived amino acid sequence indicates that the 9 kDa polypeptide is initially synthesised with an N-terminal leader sequence of 44 amino acids to direct it across the thylakoid membrane. The leader sequence consists of a positively charged N-terminal region, a long hydrophobic region and a typical cleavage site. These features have analogous counterparts in the thylakoid-transfer domain of lumenal polypeptides from chloroplasts of higher plants. These findings support the view of the proposed function of this domain in the two-stage processing model for import of lumenal, nuclear-encoded polypeptides. In addition, there is striking primary sequence homology between the leader sequences of the 9 kDa polypeptide and those of alkaline phosphatase (from the periplasmic space of Escherichia coli) and, particularly in the region of the cleavage site, the 16 kDa polypeptide of the oxygen-evolving apparatus in the thylakoid lumen of spinach chloroplasts.     

Associations between gastropod shell characteristics and egg production in the hermit crab Pagurus longicarpus

Summary Two populations (salt marsh and seagrass bed) of the hermit crab Pagurus longicarpus were sampled to examine associations between shell characteristics and egg production. Multivariate statistical analyses controlled for crab size and time of year, variables that otherwise could be confounded with shell effects. Although correlations between shell characteristics and reproduction existed in both populations, generalizations could not be made because associations varied within and between populations. Shell species was not associated with a female's reproductive state (i.e., whether or not she was barren when sampled) in either population. In the seagrass population, medium-large and large females occupying severely damaged or fouled shells were half as likely to be reproductive as females occupying other shell conditions. However, there was no association between shell condition and reproductive state for small and small-medium females in the seagrass population or among all females in the salt marsh population. In the seagrass population, small through medium-large reproductive females occupied shells more similar to their predicted shell size, regardless of whether the occupied shell was relatively small or large, than nonreproductive females. In contrast, relative shell sizes of reproductive and nonreproductive females were similar for large females in the seagrass population and all females in the salt marsh population. Clutch sizes were enhanced for females occupying Polinices duplicatus shells or shells larger than their predicted shell size in the seagrass population. Relative shell size also was associated with clutch size in the salt marsh population, but crabs occupying shells similar to their predicted shell size had the largest clutches.     

Genomic organization of the ribosomal DNA of sorghum and its close relatives

Summary The structure and organization of the ribosomal DNA (rDNA) of sorghum (Sorghum bicolor) and several closely related grasses were determined by gel blot hybridization to cloned maize rDNA. Monocots of the genus Sorghum (sorghum, shattercane, Sudangrass, and Johnsongrass) and the genus Saccharum (sugarcane species) were observed to organize their rDNA as direct tandem repeats of several thousand rDNA monomer units. For the eight restriction enzymes and 14 cleavage sites examined, no variations were seen within all of the S. bicolor races and other Sorghum species investigated. Sorghum, maize, and sugarcane were observed to have very similar rDNA monomer sizes and restriction maps, befitting their close common ancestry. The restriction site variability seen between these three genera demonstrated that sorghum and sugarcane are more closely related to each other than either is to maize. Variation in rDNA monomer lengths were observed frequently within the Sorghum genus. These size variations were localized to the intergenic spacer region of the rDNA monomer. Unlike many maize inbreds, all inbred Sorghum diploids were found to contain only one rDNA monomer size in an individual plant. These results are discussed in light of the comparative timing, rates, and modes of evolutionary events in Sorghum and other grasses. Spacer size variation was found to provide a highly sensitive assay for the genetic contribution of different S. bicolor races and other Sorghum species to a Sorghum population.     

Diurnal water storage in the stems of Picea sitchensis (Bong.) Carr.

Abstract. Two models of the relationship between diurnal variation in shoot water potential and transpiration in 14-year-old Picea sitchensis (Bong.) Carr. were compared. The first model was a physiologically based resistance-capacitance (R-C) analogue with its associated differential equations. The second was a non-physiological discrete-difference (D-D) or stochastic transfer function model. The RC model included only the effect of water storage in the phloem and bark while the D-D model implicity included all storage mechanisms. The R-C and D-D models explained similar fractions (62% and 68% respectively) of the variation in shoot water potential due to diurnal changes in transpiration rate. However, the D-D model had fewer parameters than the R-C model. The results from the D-D model showed that the resistance to flow from soil to shoots along the trunk, (RT), was 5 × 10³ MPa kg^-1s and the capacitance of the phloem and bark treated as a single store, (C_s), was 1.6 kg MPa^-1. It is suggested that the resistance to flow into storage (R_s) is much greater than R_T and can be disregarded. A non-linear version of the D-D model suggested [hat resistance to flow in the trunk increases with increasing transpiration rate.     

Subunit-specific monoclonal antibodies to tarantula hemocyanin,and a common epitope shared with calliphorin

Summary Three murine hybridoma cell lines secreting IgG₁ antibodies to 4×6 tarantula (Eurypelma californicum) hemocyanin were isolated, and the monoclonal antibodies Ec-7, Ec-8 and Ec-24 characterized by immunoblotting, immunoelectrophoresis and ELISA. WholeEurypelma hemocyanin, and the isolated subunitsa tog served as probes. For the subunits a novel, quick purification scheme on FPLC combined with immuno-affinity chromatography was established.Additionally, two cell lines secreting IgM antibodies were isolated. These antibodies showed irrelevant cross reactivities.Ec-7 strongly reacts with subunitd and weakly withb. Ec-8 and Ec-24 are specifically directed againstEurypelma subunitsa ande, respectively. The epitopes of Ec-7 and Ec-8 are sequence-dependent, whereas the Ec-24 epitope is conformation-dependent. Ec-8 and Ec-24 are specific forEurypelma hemocyanin. Ec-7 is not reactive to crustacean, centipede or gastropod hemocyanins, but binds to scorpion hemocyanin and to the immunological correlates of subunitsd andf in the hemocyanins of the spiderCupiennius salei and the xiphosuranLimulus polyphemus.In immunoblots with different polyclonal antisera,Eurypelma andAstacus hemocyanin cross-reacted with calliphorin, a larval serum protein from the blowflyCalliphora vicina. Calliphorin and chelicerate hemocyanins share the Ec-7 epitope. Sedimentation coefficients, pH stability regions, subunit size, and electron microscopical appearance of calliphorin are indiscernable from a typical 1×6 arthropod hemocyanin. This relationship is discussed in the context of hemocyanin evolution.Abbreviations FPLC fast performance liquid chromatography - PAGE polyacrylamide gel electrophoresis - SDS sodium dodecyl sulphate A preliminary account of this work was presented in June 1987 at the annual meeting of the Deutsche Zoologische Gesellschaft at Ulm (Markl 1987a)     

On the solution of mathematical models of herd immunity in human helminth infections

The general solution of the mathematical model of herd immunity to human helminth infections recently proposed by Anderson and May [3] is obtained. The numerical solution of a more accurate biological model is indistinguishable from the corresponding exact solution of a more tractable mathematical model. Computer simulations of some particular cases of this model support the notion that both ecological and immunological factors determine the observed convex patterns of age-prevalence and age-intensity curves of human helminth infections.This work was made thanks to the advise and support of Dr. Robert M. May while the author was Postdoctoral Fellow at Princeton University     

Relationships among recent models for insect population dynamics with variable rates of development

A classification scheme for those population models which allow variation in development rates is proposed, based on two ways of modifying standard age-structured models. The resulting classes of models are termed development index models and sojourn time models. General formulations for the two classes of models are developed from two basic balance equations, and numerous specific models from the literature are shown to fit into the scheme. Concepts from competing risks theory are shown to be important in understanding the interplay between mortality and maturation. Relationships among the classes are investigated both for the most general forms of the models and for the simpler forms often used. The scheme can provide guidance in developing appropriate insect population models for specific modelling situations.Contribution 3878871     

Models for contact-mediated pattern formation: cells that form parallel arrays

Kinetic continuum models are derived for cells that crawl over a 2D substrate, undergo random reorientation, and turn in response to contact with a neighbor. The integro-partial differential equations account for changes in the distribution of orientations in the population. It is found that behavior depends on parameters such as total mass, random motility, adherence, and sloughing rates, as well as on broad aspects of the contact response. Linear stability analysis, and numerical, and cellular automata simulations reveal that as parameters are varied, a bifurcation leads to loss of stability of a uniform (isotropic) steady state, in favor of an (anisotropic) patterned state in which cells are aligned in parallel arrays.     

Fumarate reduction systems in members of the family Rhodospirillaceae with different quinone types

Nineteen established and one undesignated species of the Rhodospirillaceae were examined for fumarate reduction in connection with their quinone systems. The fumarate reductase activity with reduced methyl viologen (MVH) or FMNH₂ as electron donor was found in membrane (chromatophore) preparations from phototrophically grown cells of all species containing menaquinone (MK) and/or rhodoquinone. The species having ubiquinone as the sole quinone contained no fumarate reductase activity, except some Rhodobacter species showing the FMNH₂-dependent activity. The MVH-fumarate reductase activity of the MK-type species was not inhibited by Triton X-100 or acetone treatment, suggesting the presence of a fumarate reductase reacting directly with MVH, while such an enzyme was absent in the MK-lacking strains, with few exceptions. The FMNH₂-fumarate reduction system was abolished by a detergent or acetone extraction in all bacteria but differed much among species with different quinone types as to the response to respiratory inhibitors. These differences in fumarate-reducing properties and quinone systems among the phototrophic bacteria are discussed from evolutionary and taxonomic viewpoints.Non-standard abbreviations RQ rhodoquinone - MK menaquinone - MVH reduced methyl viologen - HOQNO 2-n-heptyl-4-hydroxyquinoline-N-oxide - TTFA 2-thenoyltrifluoroacetone