Localization of the major ethidium bromide binding site on tRNA.

Binding of ethidium bromide to Escherichia coli tRNAVal and an RNA minihelix based on the acceptor stem and T-arm of tRNAVal was investigated by 19F and 1H NMR spectroscopy of RNAs labeled with fluorine by incorporation of 5-fluorouracil. Ethidium bromide selectively intercalates into the acceptor stem of the tRNAVal. More than one ethidium bromide binding site is found in the acceptor stem, the strongest between base pairs A6:U67 and U7:A66. 19F and 1H spectra of the 5-fluorouracil-substituted minihelix RNA indicate that the molecule exists in solution as a 12 base-paired stem and a single-stranded loop. Ethidium bromide no longer intercalates between base pairs corresponding to the tRNAVal acceptor stem in this molecule. Instead, it intercalates between base pairs at the bottom of the long stem-loop structure. These observations suggest that ethidium bromide has a preferred intercalation site close to the base of an RNA helical stem.     

Quantitative separation of 4-hydroxyproline from skeletal muscle collagen by micellar electrokinetic capillary electrophoresis

The phenylthiohydantoin (PTH) derivatives of 3- and 4-hydroxyproline (Hyp) were separated using micellar electrokinetic capillary electrophoresis (MEKC). The separation protocol was also used to determine Hyp content of bovine skeletal perimysial collagen preparations and whole muscle samples. Amino acids from hydrolyzed tissues were labeled using a two step procedure that involved initial reaction with o-phthalaldehyde (OPA) to modify primary amines followed by their precipitation under acidic conditions. In the second step, imino acids were reacted with phenyl isothiocyanate (PITC). This labeling method was rapid and the Hyp values determined in these biological samples were found to be in close agreement with conventional methods and other published reports.     

DOMOIC ACID PRODUCTION IN NITZSCHIA SP. (BACILLARIOPHYCEAE) ISOLATED FROM A SHRIMP-CULTURE POND IN DO SON, VIETNAM

Domoic acid (DA), a neuroexcitatory amino acid, was detected in batch culture of the newly recognized species Nitzschia navis-varingica Lundholm et Moestrup . The production of DA by this diatom was confirmed by electrospray ionization mass spectrometry. The diatom was collected from a shrimp-culture pond in Do Son, Vietnam. The production of DA (1.7 pg·cell ^{− 1}) is within the levels reported for Pseudo-nitzschia multiseries (Hasle) Hasle. The DA production started during the late exponential growth phase and reached a maximum during the early stationary growth phase. Maximum DA levels in the axenic culture decreased to about half that of the nonaxenic culture (0.9 pg·cell ^{− 1} vs. 1.7 pg·cell ^{− 1}), suggesting that DA production by the new species is influenced by bacteria.     

The Distribution and Effects of Genes Causing F(1) Weakness in ORYZA BREVILIGULATA and O. GLABERRIMA

Weakness of F₁ plants is frequently found in hybrids between strains of Oryza breviligulata (wild) and O. glaberrima (cultivated rice) endemic to West Africa. A set of two complementary dominant weakness genes, W₁ and W₂, was found to control the observed F₁ weakness. Many breviligulata strains had W₁, while most of the glaberrima and semi-wild strains had W₂ or were free of both. In the weak F₁ plants, tissue differentiation in adventitious roots seemed to be disturbed. Modifier genes affecting the expression of the weakness genes appear to be present also.