The genus Pyrus L. (Rosaceae) in south-west Europe and North Afkica

A multivariate morphometric study of the genus Pyrus in south-west Europe and North Africa shows that five species may be recognized in the area: P. bourgaeana Decne., P. communis L., P. cordata Dew., P. spinosa Forssk, and P. nivalis Jacq. Some valuable characters for identification of these species are proposed. In particular the width of fruit peduncle, petal size, leaf width and petiole length served to discriminate the taxa. Several names such as P. gharbiona Trab., P. cossonii Rehder (|M= P. longipes Balansa ex Coss. & Durieu) and P. boisseriana Buhse, are regarded as synonyms of P. cordata , while P. marnormis Trab. of P. bourgaeana. Consequently a check-list and a key to these species are provided.     

Cultured endothelial cells produce heparinlike inhibitor of smooth muscle cell growth

Using cultured cells from bovine and rat aortas, we have examined the possibility that endothelial cells might regulate the growth of vascular smooth muscle cells. Conditioned medium from confluent bovine aortic endothelial cells inhibited the proliferation of growth-arrested smooth muscle cells. Conditioned medium from exponential endothelial cells, and from exponential or confluent smooth muscle cells and fibroblasts, did not inhibit smooth muscle cell growth. Conditioned medium from confluent endothelial cells did not inhibit the growth of endothelial cells or fibroblasts. In addition to the apparent specificity of both the producer and target cell, the inhibitory activity was heat stable and not affected by proteases. It was sensitive flavobacterium heparinase but not to hyaluronidase or chondroitin sulfate ABC lyase. It thus appears to be a heparinlike substance. Two other lines of evidence support this conclusion. First, a crude isolate of glycosaminoglycans (TCA-soluble, ethanol-precipitable material) from endothelial cell-conditioned medium reconstituted in 20 percent serum inhibited smooth muscle cell growth; glycosaminoglycans isolated from unconditioned medium (i.e., 0.4 percent serum) had no effect on smooth muscle cell growth. No inhibition was seen if the glycosaminoglycan preparation was treated with heparinase. Second, exogenous heparin, heparin sulfate, chondroitin sulfate B (dermatan sulfate), chondroitin sulfate ABC, and hyaluronic acid were added to 20 percent serum and tested for their ability to inhibit smooth muscle cell growth. Heparin inhibited growth at concentrations as low as 10 ng/ml. Other glycosaminoglycans had no effect at doses up to 10 μg/ml. Anticoagulant and non- anticoagulant heparin were equally effective at inhibiting smooth muscle cell growth, as they were in vivo following endothelial injury (Clowes and Karnovsk. Nature (Lond.). 265:625-626, 1977; Guyton et al. Circ. Res. 46:625-634, 1980), and in vitro following exposure of smooth muscle cells to platelet extract (Hoover et al. Circ. Res. 47:578-583, 1980). We suggest that vascular endothelial cells may secrete a heparinlike substance in vivo which may regulate the growth of underlying smooth muscle cells.     

The influence of single base triplet changes on the stability of a pur.pur.pyr triple helix determined by affinity cleaving.

The influence of sixteen base triplet changes at a single position within a pur.pur.pyr triple helix was examined by affinity cleaving. For the 15 base pair target site studied here, G.GC, A.AT and T.AT triplets stabilize a triple helix to a greater extent than the other 13 natural triplets (pH = 7.4, 25 degrees C). Weaker interactions were detected for the C.AT, A.GC and T.CG triplets. The absence of specific, highly stabilizing interactions between third strand bases and the CG or TA base pairs demonstrates a current sequence limitation to formation of this structure. Models for the two dimensional base triplet interactions for all possible 16 natural triplets are presented.     

Influence of pH on the equilibrium association constants for oligodeoxyribonucleotide-directed triple helix formation at single DNA sites.

The energetics of oligodeoxyribonucleotide-directed triple helix formation for the pyrimidine.purine.pyrimidine structural motif were determined over the pH range 5.8-7.6 at 22 degrees C (100 mM Na+ and 1 mM spermine) using quantitative affinity cleavage titration. The equilibrium binding constants for 5'-TTTTTCTCTCTCTCT-3' (1) and 5'-TTTTTm5CTm5CTm5CTm5CTm5CT-3' (2, m5C is 2'-deoxy-5-methylcytidine) increased by 10- and 20-fold, respectively, from pH 7.6 to 5.8, indicating that the corresponding triple-helical complexes are stabilized by 1.4 and 1.7 kcal.mol-1, respectively, at the lower pH. Replacement of the five cytosine residues in 1 with 5-methylcytosine residues to yield 2 affords a stabilization of the triple helix by 0.1-0.4 kcal.mol-1 over the pH range 5.8-7.6. An analysis of these data in terms of a quantitative model for a general pH-dependent equilibrium transition revealed that pyrimidine oligonucleotides with cytidine and 5-methylcytidine form local triple-helical structures with apparent pKa's of 5.5 (C+GC triplets) and 5.7 (m5C+GC triplets), respectively, and that the oligonucleotides should bind to single sites on large DNA with apparent affinity constants of approximately 10(6) M-1 even above neutral pH.     

Subcellular localization of DNA-binding protein BA by immunofluorescence and immunoelectron microscopy

Nonhistone protein BA has been shown to decrease in amount in the chromatin of growth- stimulated normal rat liver (Yeoman et al. 1975. Cancer Res. 35:1249-1255) and in mitogen-stimulated normal human lymphocytes (Yeoman et al. 1976. Exp. Cell Res. 100:47- 55.). Subsequently, protein BA was purified and was shown to prefer to bind to double- stranded A-T-rich DNAs (Catino et al. 1978. Biochemistry. 17:983-987.). Immunization of rabbits with highly purified protein BA has resulted in the production of a specific antibody. A specific immunoreactivity for chromosomal protein BA has been demonstrated by immunoelectrophoresis and double antibody immunoprecipitation analysis with rabbit anti-BA immunoglobulin and IgG fractions. Light microscope examination of normal rat liver crysections by the indirect immunofluorescence procedure has demonstrated a cytoplasmic as well as a nuclear localization for protein BA with a pronounced perinucleolar fluorescence. Immunoelectron microscopy employing the peroxidase antiperoxidase method of antigen localization has confirmed the immunofluorescence data and has show a heterochromatin localization for protein BA. The relationship of the localization of protein BA to gene control in quiescent cells or to configurations of heterochromatin as well as the marked reduction in the amounts of protein BA which occur in stimulated growth states remains to be defined.