FURTHER ANALYSIS OF OENOTHERA BIENNIS POPULATIONS FOR INCOMPATIBILITY ALLELES

The complex-heterozygotes of Oenothera biennis are characterized by an incompatibility allele system which acts as a part of the balanced lethal mechanism. A survey was made to determine the number and frequency of different incompatibility alleles in populations throughout south central Ohio and Indiana and in one population in northern Kentucky. No single population was found to possess more than two different alleles. Within the geographic area specified, however, at least eight different alleles occurred among the various population samples. If the incompatibility alleles are a valid index of variability for the complexes which carry them, these results suggest that individual populations are fairly uniform genetically and probably arise from relatively few colonizers. The various alleles found in these populations are believed to be relics of structurally homozygous self-incompatible progenitors which hybridized with structurally homozygous, but segmentally distinctive, self-compatible forms to give rise to the complex-heterozygotes.     

Comparative Metabolism of Fluorinated 3,4-Dihydroxyphenylalanine Isomers in Aggregating Brain Cell Cultures

Fluorinated analogues of 3,4-dihydroxyphenylalanine (DOPA) were tested for intracellular metabolic conversion in aggregating cell cultures prepared from fetal rat brain. 5-Fluoro-D/L-DOPA was methylated almost exclusively to 3-O-methyl-5-fluoro-D/L-DOPA. Metabolism of 6-fluoro-D/L-DOPA resulted in 6-fluorodopamine, 6-fluoro-3,4-dihydroxyphenylacetic acid, and 3-O-methyl-6-fluoro-D/L-DOPA, but with a qualitatively and quantitatively different metabolite pattern compared with that of L-DOPA and D/L-DOPA, respectively. Homovanillic acid and fluorohomovanillic acid have not been found intracellularly in the cultures. On the basis of these data, the model development of the cerebral metabolism of tracers used in positron emission tomography can be improved.     

Kinetic mechanism for stimulation by monovalent cations of the amidase activity of the plasma protease bovine activated protein C

A study of the effect of monovalent cations on the steady-state kinetic parameters for the hydrolysis of the synthetic substrate N alpha-benzoyl-L-arginine-p-nitroanilide by activated bovine plasma protein C (APC) has been undertaken. The enzyme displayed a strict requirement for monovalent cations in its expression of amidolytic activity toward this substrate. Analysis of the variation in initial hydrolytic reaction rates, as a function of metal ion concentrations, suggested that at least two cation sites, or classes of sites, were necessary for catalysis to occur. After examination of the rate equations consequential to many different enzymic mechanisms that could account for these kinetic data, a mechanism was developed that fit the great majority of the experimental observations. In this mechanism it is postulated that cations bind to the enzyme in pairs, with a kinetically observable single binding constant, either preceded by or followed by binding of substrate. Catalysis occurs only after the enzyme-(metal cation)2-substrate complex is assembled. Some physical support for this mechanism was obtained upon the discovery that the binding (dissociation) constant for a competitive inhibitor of APC, p-aminobenzamidine, as determined by kinetic methodology, was independent of the concentration of Na+ and Cs+.     

Modular structure of a chicken lysozyme silencer: involvement of an unusual thyroid hormone receptor binding site

Silencer elements, by analogy to enhancer elements, function independently of their position and orientation. We show that the chicken lysozyme silencer S-2.4 kb has many other characteristics in common with enhancer elements. The silencer is comprised of modules that independently repress gene activity--repression being increased synergistically when different or identical modules are combined. Repression is effective both on a complete and on a minimal promoter consisting of a TATA box only. One silencer module is bound in vitro by a 75-93 kd protein, termed NeP1; the other can be bound either by the product of the oncogene v-erbA or by the thyroid hormone receptor. This erbA binding site is unusual in that the palindromic sequence is inverted.     

Chrysophyte cysts in 36 Canadian high arctic ponds

Chrysophyte stomatocysts were described from the surface sediments and other habitats (moss, rocks, and open water) of 36 ponds located on Cape Herschel, Ellesmere Island in the Canadian high Arctic (78°37'N). Thirty-five distinct stomatocyst types were described using scanning electron microscopy (SEM); 1 other cyst was common, but was not observed with SEM. Our study ponds were diverse limnologically and contained distinct cyst floras, but the cause(s) of the floristic differences are as yet unclear. Two ponds with extreme values of water chemistry (i.e. high salinity and low pH) supported unique cyst floras. Distinctive cyst floras were also observed in ponds with high nutrient input from nesting birds and/or with diverse microhabitats (e.g. moss banks), which may provide substrate for periphytic chrysophytes. Arctic pond cyst floras are typically less diverse than those from temperate regions. Highly ornamented cysts are also less common in arctic waters, but the reason for this is unknown. Stomatocysts could be used to augment paleolimnological research in arctic ponds, if the environmental factors controlling cyst distributions and possibly degree of ornamentation can be elucidated.     

Initiation of Antiviral B Cell Immunity Relies on Innate Signals from Spatially Positioned NKT Cells

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