The Evolution of MHC Diversity by Segmental Duplication and Transposition of Retroelements

Sequence analysis of a 237 kb genomic fragment from the central region of the MHC has revealed that the HLA-B and HLA-C genes are contained within duplicated segments peri-B (53 kb) and peri-C (48 kb), respectively, and separated by an intervening sequence (IF) of 30 kb. The peri-B and peri-C segments share at least 90% sequence homology except when interrupted by insertions/deletions including Alu, L1, an endogenous retrovirus, and pseudogenes. The sequences of peri-B, IF, and peri-C were searched for the presence of Alu elements to use as markers of evolution, chromosomal rearrangements, and polymorphism. Of 29 Alu elements, 14 were identified in peri-B, 11 in peri-C, and 4 in IF. The Alu elements in peri-B and peri-C clustered phylogenetically into two clades which were classified as ``preduplication' and ``postduplication' clades. Four Alu J elements that are shared by peri-B and peri-C and are flanked by homologous sequences in their paralogous locations, respectively, clustered into a ``preduplication' clade. By contrast, the majority of Alu elements, which are unique to either peri-B or peri-C, clustered into a postduplication clade together with the Alu consensus subfamily members ranging from platyrrhine-specific (Spqxcg) to catarrhine-specific Alu sequences (Y). The insertion of platyrrhine-specific Alu elements in postduplication locations of peri-B and peri-C implies that these two segments are the products of a duplication which occurred in primates prior to the divergence of the New World primate from the human lineage (35–44 mya). Examination of the paralogous Alu integration sites revealed that 9 of 14 postduplication Alu sequences have produced microsatellites of different length and sequence within the Alu 3′-poly A tail. The present analysis supports the hypothesis that HLA-B and HLA-C genes are products of an extended segmental duplication between 44 and 81 million years ago (mya), and that subsequent diversification of both genomic segments occurred because of the mobility and mutation of retroelements such as Alu repeats. Received: 21 May 1997 / Accepted: 9 July 1997     

Dioecy in the endemic genusDendrocacalia (Compositae) on the Bonin (Ogasawara) Islands

Dendrocacalia crepidifolia Nakai (Compositae, Senecioneae), the only species of this arboreal genus endemic to Haha Island in the Bonin Islands, was found to be dioecious. Male flowers differ from female ones in having a stunted style (style in female exserted from corolla and deeply bifurcating) and anthers filled with fertile pollen (anthers in the female lacking pollen). The size of the corolla and number of florets per head were similar between male and female flowers. The crown area of this arboreal species was also similar in male and female plants. The sex ratio was 0.55 male, not significantly different from 0.5. Both sexes produced nectar of similar sugar concentration (ca. 50%). The flowers are pollinated by feral honeybees (Apis mellifera), but they are thought to have been pollinated by small, lesshairy, endemic solitary bees before honeybees were introduced and subsequently became the dominant bee species on the island. The evolution of dioecy ofDendrocacalia on the island is thought to stem from the deleterious effects of inbreeding that are inherent in plants with geitonogamy. The increased geitonogamy on the island has resulted from increased woodiness (i.e., increased number of flowers per plant) and the original dependence on endemic bee pollinators, which are now endangered.     

Protein which interacts with a stimulatory factor of RNA polymerase II of Ehrlich ascites tumor cells

When partially purified Ehrlich ascites tumor RNA polymerase II was further purified on a column of phosphocellulose, stimulation of its catalysis of RNA synthesis by stimulatory factor S-II was greatly decreased. This decrease in sensitivity to the stimulatory factor was reversible: the enzyme eluted from phosphocellulose became sensitive to the factor when mixed with a protein fraction eluted from the phosphocellulose at high salt concentration. Evidence was obtained that this protein, named helper protein, binds, to the enzyme eluted from phosphocellulose, causing it to recover sensitivity to stimulatory factor S-II.     

Purification and comparison of quail and chicken pepsinogens]

Pepsinogens of quail and chick, specific to adult proventriculus, were purified and their properties were compared. These two pepsinogens are similar in regard to enzymological characters, amino acid compositions, and immunological characters.     

Studies on Thin-Layer Chromatography after Incubation with [35S]Methionine as an Aid to Identification of Mycobacteria

Thin-layer chromatography (TLC) of ethyl ether-ethanol extracts of mycobacteria obtained after incubation with [³⁵S] methionine is useful for differentiation among mycobacterial species, as the distribution of radioactive spots in TLC shows a characteristic pattern except for a few species, including M. intracellulare and M. gordonae. Some supplementary studies have been carried out in the present investigation and the following results have been obtained.

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Location of Lyb-2 on mouse chromosome 4

TheLyb-2 locus responsible for the B-lymphocyte alloantigen system Lyb-2 is located on chromosome 4 at a distance of 20.6±4.9 map units fromPgm-2. A three-point cross indicated the orderLyb-2: Mup-1b Pgm-2.     

Isolation and identification of substances inducing formation of tracheary elements in cultured carrot-root slices

Data are presented on the cytokinin status of seeds and seed components, at different stages of development in Phaseolus coccineus L., as determined with the soybean callus growth bioassay: A change in cytokinin types according to developmental stage occurred: from biologically very active less polar types (zeatin=Z) at early stages to more polar types (zeatin glucoside=Z₉G and zeatin riboside=Zr), with relatively low biological activity, at intermediate and late stages of seed development: When cytokinins were analyzed separately in embryos (embryo proper) and suspensors at two embryonic stages: heart-shaped (A) and middle cotyledonary embryos (stage B) respectively, it was found that: i) at stage A, the suspensor showed cytokinin activity at the level of Z, 2iPA (2-isopentenyladenosine) and Zr, whereas more polar cytokinins (Z₉G, Zr) were present in the embryo; ii) at stage B, when the embryo seems to become autonomous for cytokinin supply, there was a relative abundance of active cytokinins (Z, 2iPA) in the embryo to which Z₉G activity in the suspensor corresponded. It is concluded that the suspensor plays an essential role in embryogenesis by acting as a hormone source to the early embryo.Abbreviations GA gibberellic acid - 2iPA 2-isopentenyladenosine - Stage A heart-shaped embryo - siage B middle cotyledonary embryo - Z zeatin - Z₉G zeatin glucoside - Zr Zeatin riboside     

Effect of 7-fluoro prostacyclin,a stable prostacyclin analogue,on cAMP accumulation and prostaglandin binding in mastocytoma P-815 cells

The effect of 7-fluoro proscyclilin (PGI₂-F), a chemically stable analogue of prostacyclin, on cAMP accumulation in and [³H]PGE binding to mastocytoma P-815 cells was compared with those of the Na salt and methyl ester of prostacyclin (PGI₂Na or PGI₂Me), which are rapidly inactivated in aqueous solution or metabolized in the tissue.PGIF was as effective as PGI₂Me, and slightly less effective than PGI₂Na in stimulating cAMP accumulation in mastocytoma cells and rabbit platelets. PGI₂F was also more stable than PGI₂Me or PGI₂Na, and retained its original cAMP elevating activity even after incubation with or without cells for 4 h at 37°C. Cells which had been exposed to PGI₂F and then washed free of unbound reagent continued to produced cAMP for more than 3 h. PGI₂F was also as effective as PGE₁ or PGE₂ in displacing [³H]PGE₂ bound to the cells. Non-competitive inhibition by PGI₂F or PGI₂Me of [³H]PGE₂ binding to the cells, with apparent K_is of 1.29 μM and 1.13 μM, respectively, indicates the presence of different receptors for PGE₂ and for PGI₂F or PGI₂Me in mastocytoma P-815 cells.