DNA topoisomerase I from calf thymus mitochondria is associated with a DNA binding, inner membrane protein.

During purification of the type I DNA topoisomerase from calf thymus mitochondria, two polypeptides, p78 and p63, cofractionate with the enzymatic activity (Lazarus et al., (1987) Biochemistry 26, 6195-6203). The two polypeptides are released from a mitochondrial inner membrane preparation by nonionic detergent lysis and both adsorb strongly to a single-stranded DNA agarose column. We have attempted to characterize the relationship between these two polypeptides and have found the following: (i) the mitochondrial topoisomerase is active in free (monomer) and associated (heterodimer) form; (ii) the catalytic activity resides solely in p78, as adjudged by both the covalent linkage of the enzyme to substrate DNA and the ability of the enzyme to relax supercoils; (iii) at low ionic strength the enzyme is active in monomer form with p78 alone being sufficient for activity; (iv) in high salt, the high molecular weight species is a 140-kDa heterodimer composed of one p78 and one p63; and (v) the two polypeptides are not structurally related as digestion with V8 protease results in distinct proteolytic fragment patterns. These results suggest that p63 may have an important role in the metabolism of the mitochondrial topoisomerase.     

Pollination Ecology of Pedicularis megalantha D. Don (Scrophulariaceae) in the Himachal Himalaya

Abstract In the summer of 1990, the pollination ecology of Pedicularis megalantha was studied in the montane-subalpine spruce-fir forest zone (2750-3050 m) on the north slope of Mt. Huttoo at Narkanda, Himachal Pradesh, in the Indian Himalaya. Its yellow, long-tubed, nectarless flower with a curled rostrum overarched by a broad, inverted lower corolla lip was pollinated exclusively by Bombus albopleuralis and B. tunicatus workers hanging inverted from the corolla and vibrating pollen from introrse anthers concealed within the galea and releasing pollen through a small ventral opening in the galea base. The stigma, protruding from the tip of the rostrum, contacted pollen deposited on the ventral side of the insect's thorax. Corbicular pollen loads from P. megalantha pollinators indicated equal numbers of monolectic and oligolectic foragers. P. megalantha appeared to suffer from competition for pollinators by Cynoglossum wallichii at one site but to be favored in a mixed plant community with nectariferous species offering a forage resource complementary to Pedicularis pollen. As in P. punctata , the long, nectarless corolla tube of P. megalantha appears to function in extending the rostrate vibration pollination mechanism beyond the plant's foliage, which would interfere with its function. It is not an adaptation for nectar-foraging lepidopteran pollinators. P. megalantha was also found to be a root hemiparasite.     

Identification of yeasts from the suwannee river Florida estuary

The yeast flora of the Suwannee River estuary in Florida has been studied. The predominant genera were Candida and Rhodotorula; however, the yeast most frequently isolated was Cryptococcus laurentii. Nine ascosporogenous species were isolated, with Hansenula saturnus predominating. The salinity range of the sediments was 0.4 to 20.6%; in the estuary water, 0.07 to 0.25%; and in the open Gulf of Mexico, 18 to 20%.     

The biosynthesis of glucagon in perfused rat pancreas

The biosynthesis of glucagon was studied by using the recirculated, isolated perfused rat pancreas. [³H]Tryptophan was initially incorporated into acid–ethanol-extractable protein, which on gel filtration was eluted with a molecular weight of about 9000 and contained a small amount of glucagon immunoreactivity. With longer incubation [³H]tryptophan incorporation into a second peak was obtained in an identical position with that of the majority of rat glucagon immunoreactivity. This peak of labelled protein exhibited migration characteristics on polyacrylamide-gel electrophoresis identical with those of rat glucagon and was identified as newly synthesized glucagon by demonstration of specific binding and dissociation behaviour with glucagon antibodies. The incorporation of [³H]tryptophan into acid–ethanol-extractable protein was inhibited by cycloheximide. High concentrations of glucose increased [³H]tryptophan incorporation into high-molecular-weight protein but decreased incorporation into proteins smaller than cytochrome c. The pattern of [³H]leucine incorporation into protein was similar to that of [³H]tryptophan.     

THE POLLINATION ECOLOGY OF DICENTRA CUCULLARIA

In northeastern Iowa and southwestern Wisconsin the flowers of Dicentra cuculiarla were found to be pollinated almost exclusively by Bombus bimaculatus nectar-foraging queens, which were phenologically synchronized in their emergence from hibernation with the flower's anthesis. Cinematographic and stereophotographic evidence indicated that pollen transfer was effected by the ventral side of the insect's head and anterior thorax contacting essential flower parts and to a lesser degree by the front and middle legs contacting pollen-laden edges of the inner petals. Lepidoptera, Diptera, and small Hymenoptera occasionally encountered on the flowers were ineffective in pollination. Abundant Apis mellifera pollen-foraging workers regularly effected pollination, but being an introduced species it exhibits no naturally developed pollination adaptation to the flower. Nectar spur perforation by B. affinis nectar-foraging queens did not affect plant fertility, and this behavior was related only in part to forager tongue length. Nectar-foraging behavior of B. bimaculalus queens on the flowers was correlated with the phenological development of the annual insect colonies.     

Human epidermal plasminogen activator : Characterization, localization, and modulation

Using biochemical and immunocytochemical approaches, we have investigated the plasminogen activator (PA) of primary human epidermal cell cultures. A rabbit antibody raised against human urinary PA (urokinase) inhibited greater than or equal to 96% of the PA activity in the keratinocyte cultures. Immunoblot and double immunodiffusion analyses of keratinocyte PA with anti-urokinase antibody confirmed that epidermal PA was of the urokinase type. Immunocytochemical investigation of human keratinocyte cultures with anti-urokinase antibody revealed two characteristic staining patterns for PA. First, cells at the advancing edge of subconfluent colonies were cytoplasmically stained in a granular pattern. Similar staining was observed at the migrating edges of confluent epidermal cell cultures that had been wounded by cutting with a blade. This induction of PA staining was independent of cell division. Secondly, differentiated epidermal cells located on the surface of colonies were stained either at the plasma membrane or homogeneously throughout the cell. The highly differentiated, spontaneously shed cells were usually very heavily stained by anti-urokinase antibody. These immunocytochemical experiments suggest that PA expression is highly regulated in human epidermal cells. Specifically, PA expression appears to be related to cellular differentiation and to cell movement in expanding or wounded keratinocyte colonies.