Higher order structure of the ribosomal 5 S RNA.

The structure of the ribosomal 5 S RNA was examined using Fe(II)-EDTA, a solvent-based reagent that cleaves the phosphodiester backbone of both double- and single-stranded RNA but is restricted by the three-dimensional structure. In the yeast 5 S RNA, cleavages were significantly restricted in six specific regions of the molecule; restrictions in only two of these regions were clearly dependent on a high salt/magnesium ion environment. A comparison of four RNAs of diverse origin revealed strong similarities in the cleavage profiles supporting a highly conserved higher order structure. Taken together with previous studies these data provide a more detailed modeling of the three-dimensional structure.     

Fluorescence studies of internal rotation in apohemoglobin alpha-chains

The molecular dynamics of the apo alpha-chain of human hemoglobin have been examined using three different fluorescent probes, as well as by circular dichroism. All of these criteria are consistent with a significant loss of organized structure and molecular rigidity for the apo derivative. The apo alpha-chain thus contrasts with the apo beta-chain, which retains considerable rigidity and organized structure.     

Morphometric analysis of male genitalia in sibling species of Drosophila virilis Sturt

The structure of male genital organs in sibling species of the virilis group of Drosophila was examined using methods of multivariate statistics. The differences among these species were estimated using 33 indices and 2 angle parameters. The intraspecific and interspecific correlation structure of the examined characters and the order of their divergence were established. The key characters with respect to forming interspecific differences in the virilis species group were identified. Based on these results, the relative systematic positions of the sibling species are discussed as well as similarities and differences of the pattern of relationships among the species from that generally accepted for the virilis group.     

FINE STRUCTURE OF PETROBINAE (COMPOSITAE-HELIANTHEAE) POLLEN WALLS

Pollen of the subtribe Petrobinae (Compositae-Heliantheae) was examined by light and electron microscopy. Surface morphology and fine structure of all species examined were identical; these characters also were similar to pollen of other Heliantheae subtribes examined in previous studies.     

The radiolysis of aqueous ammonium cyanide: polymers of interest to chemical evolution studies

Some of the polymers isolated from the mixture of products obtained upon irradiation of dilute oxygen-free solutions of NH4CN with gamma rays from a 60Co source were examined. Their molecular weights were estimated to be in the range 4000-20000 daltons; elements of their structure were inferred from chemical and spectroscopic studies; and their interactions with nucleic acid components were examined. Significance of these results for chemical evolution studies is summarized.     

Egg surface structure in the annual fishes Simpsonichthys (subgenera Ophthalmolebias and Xenurolebias) and Nematolebias (Teleostei: Cyprinodontiformes: Rivulidae): variability and phylogenetic significance

The surfaces of the egg chorion of nine species of Simpsonichthys , two of Nematolebias and eight other species of rivulids were studied with scanning electron microscopy revealing details of ornamentation that were previously undocumented. Surface structures of eggs of Simpsonichthys of the subgenus Ophthalmolebias are described for the first time: eggs of Simpsonichthys constanciae , Simpsonichthys perpendicularis , Simpsonichthys rosaceus and Simpsonichthys suzarti are ornamented with a very characteristic palm-like structure, that is restricted to these species among the rivulids examined. The surface of the egg chorion of Simpsonichthys bokermanni lacks the well-developed palm-like structure, but has a characteristic conical projection, distinct from the structures of other rivulids examined, that is proposed as homologous to the palm-like structure. Simpsonichthys bokermanni shares with Nematolebias papilliferus and Nematolebias whitei the presence of concentric rows of spiny projections around the micropylar region. Species of Simpsonichthys of the subgenus Ophthalmolebias , Simpsonichthys myersi (of the subgenus Xenurolebias ), and N. whitei share the presence of large rounded protuberances on the surface of the egg chorion. The phylogenetic significance of these features are evaluated and discussed in light of current knowledge about rivulid relationships.     

Hexokinase A from mammalian brain: comparative peptide mapping and immunological studies with monoclonal antibodies

Immunological reactivity of partially purified hexokinase A (ATP:D-hexose 6-phosphotransferase, EC 2.7.1.1) from brain of several vertebrate species has been compared by using enzyme-linked immunosorbent assay and seven monoclonal antibodies raised against the rat brain enzyme. The epitopes recognized by three of these antibodies have been rather widely conserved among the species examined (rat, mouse, guinea pig, rabbit, cat, dog, sheep, cow, pig, chicken), while this was not the case for the epitopes recognized by the other antibodies, which differed markedly in their distribution among these species. The domain structure of these enzymes has been examined by peptide mapping (after limited tryptic digestion) in conjunction with immunoblotting techniques employing monoclonal antibodies. The results indicate that the overall domain structure of these enzymes is similar to that previously described for rat brain hexokinase A, but that there are significant differences in the size of these domains in enzymes from different species.     

Diversity in the oligomeric channel structure of the multidrug efflux pumps in Pseudomonas aeruginosa

MexAB-OprM, the multidrug efflux pump of Pseudomonas aeruginosa, contributes to the high resistance of this organism to a wide variety of antibiotics. To investigate the structure and function of OprM, the outer membrane channel of MexAB-OprM, we examined the oligomeric states of OprM and its homologues OprJ and OprN. These proteins were treated with crosslinking reagent after their reconstitution into liposome membranes. The crosslinked products indicated that OprM and OprN formed trimers, while OprJ unexpectedly appeared to form a tetramer. In order to test whether differences in oligomeric structure might be intimately related to channel function, we examined the channel-forming activity of these proteins by liposome swelling assay. However, no significant differences in channel characteristics were detected among OprM, OprJ, and OprN. We proposed the probable explanation for the diversity in the oligomeric structure of the channel proteins.     

Morphometric Analysis of Male Genitalia in Sibling Species of Drosophila virilis Sturt.

The structure of male genital organs in sibling species of the virilis group of Drosophila was examined using methods of multivariate statistics. The differences among these species were estimated using 33 indices and 2 angle parameters. The intraspecific and interspecific correlation structure of the examined characters and the order of their divergence were established. The key characters with respect to forming interspecific differences in the virilis species group were identified. Based on these results, the relative systematic positions of the sibling species are discussed as well as similarities and differences of the pattern of relationships among the species from that generally accepted for the virilis group.     

Probing genetic variation and glycoform distribution in lectins of the Erythrina genus by mass spectrometry

Six leguminous lectins from the seeds of plants of the Erythrina genus, namely E. caffra (ECafL), E. cristagalli (ECL), E. flabelliformis (EFL), E. lysistemon (ELysL), E. rubrinerva (ERL), and E. vespertilio (EVL), were examined to establish their sequence homology and to determine the structure and sites of attachment of their glycans. Tryptic digests of these lectins were analyzed by capillary electrophoresis coupled to electrospray mass spectrometry (CE-ESMS). Assignments were made by comparing the molecular masses of the observed tryptic peptides with those of Erythrina corallodendron lectin (ECorL), the sequence of which had been established previously. Glycan structure and genetic variations in the amino acid sequence were probed by tandem mass spectrometry. Small differences were found between the sequences of the various lectins examined and all of them exhibited C-terminal processing resulting in proteins with a C-terminal Asn residue. The major glycan of these glycoproteins was shown to be the heptasaccharide Man(3)XylFucGlcNAc(2), consistent with previous investigations on ECL and ECorL. A minor glycan heterogeneity was observed for most lectins examined except for that of ECafL and ECorL where an extra hexose residue was observed on the reducing GlcNAc residue of the heptasaccharide.     

Examining the area effect for parasite communities of bluegill x green sunfish hybrids in five constructed ponds in Kansas

The parasite communities of bluegill x green sunfish hybrids were examined from 5 constructed ponds in Kansas in an attempt to evaluate the separate effects of habitat area and habitat heterogeneity on parasite community structure. Characterization of fish community structure and collection of hybrid fishes was conducted using an electrofishing boat. Benthic invertebrates were sampled, and substrate types examined at 30 evenly spaced points in each pond. Nonmetric multidimensional scaling of the parasite infracommunities, in concert with an analysis of similarities, indicated significant clustering of infracommunities by locality. The number and diversity of habitat types, and the richness and diversity of both fishes and benthic invertebrates, were positively correlated with the first axis of the infracommunity ordination. Pond surface area, parasite richness, and stocking pressure were negatively correlated with the first axis of the infracommunity ordination, suggesting that pond area, stocking pressure, or both was a stronger determinant of parasite community structure in these systems than habitat and host heterogeneity.     

Effect of lunularic acid analogues on liverwort growth and IAA oxidation

The growth inhibitory activity of lunularic acid and a number of analogues has been examined in liverwort gemmaling and cress root growth tests. Lunularic acid was no more active than a wide range of similar compounds and no clear correlation between structure and activity was observed. The effects of these compounds, and of liverwort extracts, on in vitro IAA-oxidase activity was also examined.     

Articulation of the pelvic spine in acanthopterygian fishes,with notes on its phylogenetic implications

The pelvic spine articulation in 88 non-squamipinne acanthopterygian species belonging to 59 families and 8 orders was examined. For most acanthopterygians, the pelvic bone lacks a foramen for the attachment of the pelvic spine flanges and this structural condition is considered a primitive acanthopterygian state. Only in Caproidae, Leiognathidae, and Polynemidae among the examined species do the pelvic spine flanges fuse through a foramen in the pelvic bone and this articulation is considered most derived. In the remaining acanthopterygians examined, the pelvic spine flanges butt against each other through the pelvic foramen. However, these flanges do not fuse. This structure is considered an intermediate state. The possible phylogenetic implication of these articulating states regarding acanthopterygian phylogeny is discussed.     

Sugar Beet Pectin–Protein Complexes

The physical structure of pectin extracted from fresh sugar beet has been examined by atomic force microscopy (AFM). The images obtained reveal that these extracts contain a mixture of pectin polysaccharides and protein–pectin complexes. The AFM data demonstrate, for the first time, that these protein–pectin complexes consist of pectin molecules with protein attached to one end of the pectin chain.     

Characteristics of the genetic structure of parasite and host populations by the example of helminthes from moor frog Rana arvalis Nilsson

The genetic structure of populations of four helminth species from moor frog Rana arvalis, in comparison with the population-genetic structure of the host, has been studied with the gel-electrophoresis method. As compared with the host, parasites are characterized by more distinct deviation from the balance of genotypic frequencies and higher level of interpopulation genetic differences. The genetic variability indices in the three of four frog helminthes examined are lower than those in the host. Moreover, these indices are lower than the average indices typical of free-living invertebrates; this fact contradicts the opinion on polyhostality of these helminthes and their wide distribution.     

The inactivation of tet genes on a plasmid by the duplication of one inverted repeat of a transposon-like structure which itself mediates tetracycline resistance

Derivatives of a naturally occurring IncFII tetracycline resistance plasmid (pUB889) which are unable to confer resistance to tetracycline, and which were isolated from both partners of a married couple, have been examined. The tet genes are part of a transposon-like structure which is closely related to, but distinct from, Tn10. The lesions in the two plasmids examined are identical and involve the insertion of a nucleotide sequence of 0.9 × 10⁶ within the region encoding tetracycline resistance, expression of which is lost as a consequence. The extra DNA is homologous with the nucleotide sequence, a pair of which form the inverted repeats of the Tn10-like structure. We conclude that this nucleotide sequence comprises an IS element. The epidemiological implications arising from the origin of these plasmids are discussed.     

Community structure and seasonal dynamics of helminth parasites in Lepomis cyanellus and L. macrochirus from Charlie's Pond, North Carolina: host size and species as determinants of community structure

The community structure and seasonal dynamics of 16 helminth species infecting green (Lepomis cyanellus) and bluegill (L. macrochirus) sunfishes in Charlie's Pond, North Carolina, was examined. One hundred and fifty-four fishes including 90 green sunfish and 64 bluegill sunfish were collected between March and November 2000 and examined for the presence of helminth parasites. Five of these species underwent significant changes in abundance in green sunfish infracommunities, 3 of which also displayed seasonal changes in prevalence. Three of the 16 species fluctuated seasonally in bluegill infrapopulations; 2 also underwent changes in prevalence. Species richness and diversity varied across the 9-mo period for both host species, whereas total helminth abundance remained constant. Analysis of component communities revealed differences in community structure for the 2 host species. Bluegills were found to harbor larger and more diverse communities. Bluegills also contained larger infrapopulations of 5 species, whereas green sunfish had greater abundance of 2 species. Interpretation of these data suggests that host species and size are strongly associated with the predictability of community structure.