Structure of the serotype f polysaccharide antigen of Streptococcus mutans

The structure of the serotype f polysaccharide antigen of Streptococcus mutans was determined by methylation analysis, periodate oxidation, and partial methanolysis, and the configuration of the anomeric linkages by 13C-n.m.r. spectroscopy, indicating the trisaccharide repeating unit----3)-alpha-L-Rhap-(1----2)-[alpha-D-Glcp-(1----3)]-alpha-L-+ ++Rhap- (1----. The structure of the backbone of the polysaccharide was confirmed by demonstrating immunological identity between the product of Smith degradation of the S. mutans serotype f antigen and the group A-variant streptococcal polysaccharide.     

An attempt to estimate the predatory pressure exerted by the lesser weever, Trachinus vipera Cuvier, in the southern North Sea

In order to evaluate the impact of the lesser weever on the ecosystem of the southern North Sea, geographical distribution, density, growth, production and food requirements have been estimated. High densities were found on and around the Brown Ridge, an area with high tidal current velocities, medium grain-size of the sediment and a poor benthic fauna. Growth is restricted to the months of June October. During the winter cessation of growth a considerable loss of weight (about 20%) takes place. Mortality has been estimated by using the average size frequency distribution of all catches made from 1972 to 1984. The resulting convex type of survival curve indicates a high survival rate of the II to IV-group fishes. The production (estimated with Allen's graphical method) of a population of 100 individuals including all age groups (0-VI) amounts to 123.7 g AFDW-year'. In areas with highest densities, consequently, production amounts to 0.018–0.078 g AFDW-m² -year^-1. With an assumed transfer efficiency of 10% through the year, food requirements amounts to 0.18–0.78 g AFDW-m ² -year ^-1. Since the lesser weever feeds mainly on fish (85.6%), almost exclusively on gobies (Pomatoschistus sp.), and with an assumed transfer efficiency of approximately 10%, the indirect predatory pressure exerted by it may amount to 1.6 6.7g AFDW-m ².year ^-1. A possible feeding by gobies on pelagic organisms (calanoids, mysids) is discussed.     

Methylation and demethylation of the Arabidopsis genome

The primary sequence of the genome is broadly constant and superimposed upon that constancy is the postreplicative modification of a small number of cytosine residues to 5-methylcytosine. The pattern of methylation is non-random; some sequence contexts are frequently methylated and some rarely methylated and some regions of the genome are highly methylated and some rarely methylated. Once established, methylation is not static: it can potentially change in response to developmental or environmental cues and this may result in correlated changes in gene expression. Changes can occur passively owing to a failure to maintain DNA methylation through rounds of DNA replication, or actively, through the action of enzymes with DNA glycosylase activity. Recent advances in genetic analyses and the generation of high resolution, genome-wide methylation maps are revealing in unprecedented detail the patterns and dynamic changes of DNA methylation in plants.     

The allelic isozymes of hexose-6-phosphate dehydrogenase isolated from Fundulus heteroclitus: physical characteristics and kinetic properties

Hexose-6-phosphate dehydrogenase (H6PDH-A2; beta-D-glucose:NAD(P)+ oxido-reductase; E.C. 1.1.1.47) of the teleost Fundulus heteroclitus (L.) shows clinal allelic variation along the east coast of North America. Three of the major allelic isozymes have been purified and compared for native molecular weight, subunit molecular weight, isoelectric point, thermal stability, and steady-state kinetic properties (pH 8.0 and 25 degrees C). Significant differences were found among the allelic isozymes for isoelectric point, thermal stability, and some kinetic parameters. The predominant allelic isozyme in northern populations (H6PDH-AcAc) was found to be more sensitive to heat denaturation than were the predominant homozygous allelic isozymes isolated from southern populations (H6PDH-AaAa and H6PDH-AbAb). The H6PDH-AcAc allelic isozyme had both a significantly greater Km for glucose-6-phosphate than did either of the southern phenotypes and a significantly greater Km for NADP+ and Ki of NAD+ than did one of the southern phenotypes (H6PDH-AaAa). While the allelic isozymes are functionally nonequivalent, it is not yet known whether these differences are reflected at higher levels of biological organization.      

Cell fate in the development of the Arabidopsis flower

The Arabidopsis flower consists of four concentric whorls of organs. The first (outermost) whorl consists of four sepals and the fourth (innermost) whorl is made up of two carpels. Cell fate in the first and fourth whorls was studied using X-ray-induced yellow ch-42 sectors. Sector boundaries were found to be non-random around the two whorls and four generalizations relating the marked and unmarked tissues were deduced. In the sepal and carpel whorls the smallest sectors of marked and unmarked tissue were found to be one half of a sepal and one half of a carpel, respectively. A detailed frequency-distance map of the floral primordium was made and found to be a ridge with the fourth whorl carpels at the summit and the first whorl transverse sepal pair at the base. Consideration of: the rate of loss of chimerism in the inflorescence meristem, the frequency-distance across the flower and the frequency-distance between successive flowers, was used to produce an abstract model of the inflorescence meristem.