A rRNA-mRNA base pairing model for UGA-dependent termination.

A series of site-directed mutations has been constructed in E coli 16S rRNA and shown to suppress UGA-dependent translational termination. With the exception of the C726 to G base change, all were constructed in helix 34. Characterization of these mutations is reviewed here and from these data and mRNA-rRNA base pairing model for the termination event is presented. The interaction functions via antiparallel base pairing between either 1 of the 2 UCA motifs in helix 34 and the complementary UGA stop codon on the message, thus forming a quasicontinuous A-type helical structure that is further stabilized by stacking enthalpy. Finally, rRNA motifs potentially required for UAA and UAG-dependent translational termination are discussed.     

Effect of lactic starter cultures on the organic acid composition of milk and cheese during ripening—analysis by HPLC

The major function of lactic starter cultures in cheese making is to produce lactic and other organic acids from the carbohydrates present in milk. The activity of six starter cultures consisting of two Lactococcus lactis ssp. lactis , two Lactococcus lactis ssp. lactis biovar. diacetylactis and two Leuconostoc strains, was tested by monitoring the evolution of the organic acid composition of milk by a modified HPLC method. In addition, their performance as cheese starters was also tested. The HPLC method developed proved to be a precise tool to monitor the organic acid content. Thus, it can be used to follow the fermentation ability of starter cultures, providing information about the type of fermentation. The use of any of the six starters assayed is suggested for manufacturing Afuega'l Pitu cheese.     

A New Laboratory Technique for Studying the Effects of Heavy Metals on Bryophyte Growth

A novel, non-destructive method for measuring moss gametophytegrowth rates is presented. Standard 2-cm moss gametophores aresupported vertically on Velcro strips held within a clear perspexbox, with their bases resting in liquid. Shoots sampled fromthe field were either continuously exposed to test solutionsvia their cut bases, or by preliminary pulse-immersion. Growthwas assessed by linear extension, or final dry mass, and showeddifferent patterns and sensitivities to heavy metals using thetwo exposure methods. A biologically appropriate assessmentof toxicity was established, using tissue concentrations comparableto material from polluted field sites, by considering the cellularlocation of heavy metals in shoots. A linear relationship wasestablished between apical growth and intracellular Zn concentrationrecovered in the newly produced gametophyte tissue, irrespectiveof the method of exposure or Zn concentration in the remainingor original shoot portion. The limitations and ambiguity associatedwith many heavy-metal monitoring and toxicity studies are addressed,and the advantages and further applications offered by thisgrowth system are discussed. Rhytidiadelphus squarrosus ; growth; heavy metal effects; cadmium; copper; lead; zinc; bioassay     

Introduction: A perspective from the humanities-science boundary

The articles in this special issue range across such influences on climate as solar emissions, orbital precession, atmosphere, oceans, and precipitation, and generally approach, each in some context, human implications of these phenomena. The common underlying theme of all of the papers is the effect the phenomena have on radiation balance as measured by global average temperature. This introductory paper undertakes a formulation of radiation balance theory that makes it serviceable to students of regional science. The objective is to go beyond inference of cause and effect by correlation to causal accounts of cause and effect through regional climatic and cultural processes. This is accomplished primarily by revisualization of the energy system with regions as dependent spatiotemporal entities, and temporally through a protocol for regional episode definition.This special issue ofHuman Ecology consists of the American Anthropological Association Invited Symposium on Global Climate Change.