The vibrational spectra and structure of poly(rA-rU)-poly(rA-rU)

Infrared and Raman spectra of aqueous poly(rA-rU)·poly(rA-rU), the double-helical complex containing strands of alternating riboadenylate and ribouridylate residues, display significant differences from one another and from corresponding spectra of poly(rA)·poly(rU), the double-helical complex of riboadenylate and ribouridylate homopolymers. Parallel studies on the copolymer and homopolymer complexes by cesium sulfate density gradient centrifugation, ultraviolet absorption spectroscopy, hydrogenion titration, 1-N oxidation of adenine residues by monoperphthalic acid and X-ray diffraction reveal, however, that the geometry of base pairing between adenine and uracil is closely similar in each complex and apparently of the Watson-Crick type. Therefore the differences observed between vibrational spectra of poly (rA-rU)·poly (rA-rU) and poly(rA)·poly(rU) are not due to different base-pairing schemes but may be attributed to differences in vibrational coupling between vertically stacked bases. Vibrational coupling may also account for the differences between infrared and Raman spectra of the same complex. Thus, the present results indicate that infrared and Raman frequencies of RNA in the region 1750–1550 cm^?1 should be dependent on the base sequence.     

ECOLOGICAL BARRIERS TO GENE FLOW BETWEEN RIPARIAN AND FOREST SPECIES OF AINSLIAEA (ASTERACEAE)

Understanding the role of habitat‐associated adaptation in reducing gene flow resulting in population differentiation and speciation is a major issue in evolutionary biology. We demonstrate a significant role for habitat divergence in species isolation between two naturally hybridizing riparian and nonriparian plants, Ainsliaea faurieana and A. apiculata (Asteraceae), on Yakushima Island, Japan. By analyzing the fine‐scale population structure at six sympatric sites, we found that variations in leaf shape, geography, light conditions, and genotype were strongly correlated across riverbank–forest transitions. No evidence of effective gene flow was found between the two species across the majority of the transition zones, although the NewHybrid clustering analysis confirmed interspecific hybridization. However, a relatively high level of gene flow was observed across one zone with a more diffuse ecotone and intermediate flooding and light conditions, possibly generated by human disturbances. These results suggest that the barriers to gene flow between the riparian and forest species are primarily ecological. Additional common garden experiments indicated that the two species are adaptively differentiated to contrasting flooding and light environments. Overall, our study suggests that adaptations to different habitats can lead to the formation of reproductive isolating barriers and the maintenance of distinct species boundaries.     

Cell surface changes accompanying aging in human diploid fibroblasts : II. Two types of age-related changes revealed by concanavalin A-mediated red blood cell adsorption

Age-related changes in cell surfaces of human diploid fibroblasts (TIG-1) were investigated using the concanavalin A (ConA)-mediated red blood cell (RBC) adsorption assay. When ConA-coated RBCs were adsorbed to fibroblasts (RBC coating method), the amount of RBCs adsorbed per mg of fibroblast protein increased continuously from the early phases of cell passage up through cell senescence. On the other hand, when RBCs were adsorbed to ConA-coated fibroblasts (fibroblast coating method), RBC adsorption did not occur throughout phase II and increased with the advance of phase III. [³H]ConA binding to fibroblasts, however, did not change with aging to the extent that could explain the observed changes in RBC adsorption. These age-related characteristics in RBC adsorption and [³H]ConA binding were also observed for WI38 and IMR-90 cells. In addition, SV40- and ⁶⁰Co-transformed WI38 cells showed a close resemblance in their RBC adsorption capacity to early phase III cells.RBC adsorption with both the RBC and fibroblast coating methods was not a function of cell cycle phase and time spent in culture (metabolic time). Co-culturing of young cells with old or transformed cells did not affect the RBC adsorption capacity of respective cells. These results suggest that RBC adsorption with the RBC and fibroblast coating methods may represent cell surface markers for division age and senescence of aging human diploid cells.