Precise sequence complementarity between yeast chromosome ends and two classes of just-subtelomeric sequences

The terminal regions (last 20 kb) of Saccharomyces cerevisiae chromosomes universally contain blocks of precise sequence similarity to other chromosome terminal regions. The left and right terminal regions are distinct in the sense that the sequence similarities between them are reverse complements. Direct sequence similarity occurs between the left terminal regions and also between the right terminal regions, but not between any left ends and right ends. With minor exceptions the relationships range from 80% to 100% match within blocks. The regions of similarity are composites of familiar and unfamiliar repeated sequences as well as what could be considered “single-copy” (or better “two-copy”) sequences. All terminal regions were compared with all other chromosomes, forward and reverse complement, and 768 comparisons are diagrammed. It appears there has been an extensive history of sequence exchange or copying between terminal regions. The subtelomeric sequences fall into two classes. Seventeen of the chromosome ends terminate with the Y′ repeat, while 15 end with the 800-nt “X2” repeats just adjacent to the telomerase simple repeats. The just-subterminal repeats are very similar to each other except that chromosome 1 right end is more divergent.

Ocular cicatricial pemphigoid antigen: Partial sequence and biochemical characterization

Ocular cicatricial pemphigoid (OCP) is an autoimmune disease that affects mainly conjunctiva and other squamous epithelia. OCP is histologically characterized by a separation of the epithelium from underlying tissues within the basement membrane zone. Immunopathological studies demonstrate the deposition of anti-basement membrane zone autoantibodies in vivo. Purified IgG from sera of patients with active OCP identified a cDNA clone from a human keratinocyte cDNA library that had complete homology with the cytoplasmic domain of β4-integrin. The sera recognized a 205-kDa protein in human epidermal, human conjunctiva, and tumor cell lysates that was identified as β4-integrin by its reaction with polyclonal and monoclonal antibodies to human β4-integrin. Sera from patients with bullous pemphigoid, pemphigus vulgaris, and cicatricial pemphigoid-like diseases did not recognize the 205-kDa protein, indicating the specificity of the binding. These data strongly implicate a role for human β4-integrin in the pathogenesis of OCP. It should be emphasized that multiple antigens in the basement membrane zone of squamous epithelia may serve as targets for a wide spectrum of autoantibodies observed in vesiculobullous diseases. Molecular definition of these autoantigens will facilitate the classification and characterization of subsets of cicatricial pemphigoid and help distinguishing them from bullous pemphigoid. This study highlights the function and importance of β4-integrin in maintaining the attachment of epithelial cells to the basement membrane.

Structural aspects of activation pathways of aspartic protease zymogens and viral 3C protease precursors

The three-dimensional structures of the inactive protein precursors (zymogens) of the serine, cysteine, aspartic, and metalloprotease classes of proteolytic enzymes are known. Comparisons of these structures with those of the mature, active proteases reveal that, in general, the preformed, active conformations of the residues involved in catalysis are rendered sterically inaccessible to substrates by the residues of the zymogens’ N-terminal extensions or prosegments. The prosegments interact in nonsubstrate-like fashions with the residues of the active sites in most of the cases. The gastric aspartic proteases have a well-characterized zymogen conversion pathway. Structures of human progastricsin, the inactive intermediate 2, and active human pepsin are known and have been used to define the conversion pathway. The structure of the zymogen precursor of plasmepsin II, the malarial aspartic protease, shows a new twist on the mode of inactivation used by the gastric zymogens. The prosegment of proplasmepsin disrupts the active conformation of the two catalytic aspartic acid residues by inducing a major reorientation of the two domains of the mature protease. The picornaviral 2A and 3C proteases have a chymotrypsin-like tertiary structure but with a cysteine nucleophile. These enzymes cleave themselves from the viral polyprotein in cis (intramolecular cleavage) and carry out trans cleavages of other scissile peptides important for the virus life cycle. Although the structure of the precursor viral polyprotein is unknown, it probably resembles the organization of the proenzymes of the bacterial serine proteases, subtilisin, and α-lytic protease. Cleavage of the prosegment is known to occur in cis for these precursor molecules.

Induction of primordial germ cells from murine epiblasts by synergistic action of BMP4 and BMP8B signaling pathways

Extraembryonic ectoderm-derived factors instruct the pluripotent epiblast cells to develop toward a restricted primordial germ cell (PGC) fate during murine gastrulation. Genes encoding Bmp4 of the Dpp class and Bmp8b of the 60A class are expressed in the extraembryonic ectoderm and targeted mutation of either results in severe defects in PGC formation. It has been shown that heterodimers of DPP and 60A classes of bone morphogenetic proteins (BMPs) are more potent than each homodimers in bone and mesoderm induction in vitro, suggesting that BMP4 and BMP8B may form heterodimers to induce PGCs. To investigate how BMP4 and BMP8B interact and signal for PGC induction, we cocultured epiblasts of embryonic day 6.0–6.25 embryos with BMP4 and BMP8B proteins produced by COS cells. Our data show that BMP4 or BMP8B homodimers alone cannot induce PGCs whereas they can in combination, providing evidence that two BMP pathways are simultaneously required for the generation of a given cell type in mammals and also providing a prototype method for PGC induction in vitro. Furthermore, the PGC defects of Bmp8b mutants can be rescued by BMP8B homodimers whereas BMP4 homodimers cannot mitigate the PGC defects of Bmp4 null mutants, suggesting that BMP4 proteins are also required for epiblast cells to gain germ-line competency before the synergistic action of BMP4 and BMP8B.

Chloroplast DNA evidence of colonization, adaptive radiation, and hybridization in the evolution of the Macaronesian flora.

Most evolutionary studies of oceanic islands have focused on the Pacific Ocean. There are very few examples from the Atlantic archipelagos, especially Macaronesia, despite their unusual combination of features, including a close proximity to the continent, a broad range of geological ages, and a biota linked to a source area that existed in the Mediterranean basin before the late Tertiary. A chloroplast DNA (cpDNA) restriction site analysis of Argyranthemum (Asteraceae: Anthemideae), the largest endemic genus of plants of any volcanic archipelago in the Atlantic Ocean, was performed to examine patterns of plant evolution in Macaronesia. cpDNA data indicated that Argyranthemum is a monophyletic group that has speciated recently. The cpDNA tree showed a weak correlation with the current sectional classification and insular distribution. Two major cpDNA lineages were identified. One was restricted to northern archipelagos--e.g., Madeira, Desertas, and Selvagens--and the second comprised taxa endemic to the southern archipelago--e.g., the Canary Islands. The two major radiations identified in the Canaries are correlated with distinct ecological habitats; one is restricted to ecological zones under the influence of the northeastern trade winds and the other to regions that are not affected by these winds. The patterns of phylogenetic relationships in Argyranthemum indicate that interisland colonization between similar ecological zones is the main mechanism for establishing founder populations. This phenomenon, combined with rapid radiation into distinct ecological zones and interspecific hybridization, is the primary explanation for species diversification.

Life-span, T-cell responses, and incidence of lymphomas in congenic mice.

Survival, T-cell functions, and postmortem histopathology were studied in H-2 congenic strains of mice bearing H-2b, H-2k, and H-2d haplotypes. Males lived longer than females in all homozygous and heterozygous combinations except for H-2d homozygotes, which showed no differences between males and females. Association of heterozygosity with longer survival was observed only with H-2b/H-2b and H-2b/H-2d mice. Analysis using classification and regression trees (CART) showed that both males and females of H-2b homozygous and H-2k/H-2b mice had the shortest life-span of the strains studied. In histopathological analyses, lymphomas were noted to be more frequent in females, while hemangiosarcomas and hepatomas were more frequent in males. Lymphomas appeared earlier than hepatomas or hemangiosarcomas. The incidence of lymphomas was associated with the H-2 haplotype--e.g., H-2b homozygous mice had more lymphomas than did mice of the H-2d haplotype. More vigorous T-cell function was maintained with age (27 months) in H-2d, H-2b/H-2d, and H-2d/H-2k mice as compared with H-2b, H-2k, and H-2b/H-2k mice, which showed a decline of T-cell responses with age.