Two simple methods for the synthesis of oligonucleotides bearing a N-(2-hydroxyethyl)phenazinium (Phn) residue at the 5'- and/or 3'-terminal phosphate groups are proposed. By forming complexes between a dodecanucleotide d(pApApCpCpTpGpTpTpTpGpGpC), a heptanucleotide d(pCpCpApApApCpA), and Phn derivatives of the latter, it is shown that the introduction of a dye at the end of an oligonucleotide chain strongly stabilizes its complementary complexes. The Tmax and the thermodynamic parameters (delta H, delta S, delta G) of complex formation were determined. According to these data, coupling of a dye with the 5'-terminal phosphate group is the most advantageous: delta G(37 degrees C) is increased by 3.59 +/- 0.04 kcal/mol compared to 2.06 +/- 0.04 kcal/mol for 3'-Phn derivatives. The elongation of the linker, which connects the dye to the oligonucleotide, from a dimethylene up to a heptamethylene usually leads to destabilization of the oligonucleotide complex. The complementary complex formed by the 3',5'-di-Phn derivative of the heptanucleotide was found to be the most stable among all duplexes investigated. Relative to the unmodified complex the increase in free energy was 4.96 +/- 0.04 kcal/mol. The association constant of this modified complex at 37 degrees C is 9.5 x 10(6) M-1, whereas the analogous value for the unmodified complex is only 3 x 10(3) M-1.

Macquarie Island (Southern Ocean) is a fragment of Miocene ocean crust and upper mantle formed at a slow-spreading ridge system, uplifted and currently exposed above sea-level. The crustal rocks on the island have unusually enriched compositions and the strong signature of an enriched source requires low overall degrees of melt depletion in the underlying mantle. Peridotites on the island, however, are highly refractory harzburgites that can be modeled as residues of420^25% of near-fractional melting from which all the free clinopyroxene was melted out. The peridotites have some of the highest spinel Cr-numbers (0•40^0•49) and lowest orthopyroxenecore Al 2 O 3 concentrations (2•7^3•0 wt %) reported so far for oceanic peridotites. The peridotites were subsequently modified by melt^rock reactions underneath the Miocene ridge system. The refractory character of the peridotites is inconsistent with the slow-spreading ridge setting as well as with the enriched character of the overlying crust, and must indicate a previous depletion event; the peridotites are not the source residue of the overlying ocean crust on Macquarie Island. Osmium isotopic compositions of peridotite samples are very unradiogenic (187 Os/ 188 Os ¼ 0•1194^0•1229) compared with normal abyssal peridotites and indicate a long-lived rhenium depletion. Proterozoic rhenium-depletion ages indicate that these rocks have preserved a memory of an old mantle melting event. We argue that the Macquarie Island harzburgites are samples from an anciently depleted refractory mantle reservoir that may be globally important, but that is generally overlooked because of its sterility; that is, its inability to produce basalts. This reservoir may preserve key information about the history of the Earth' s mantle as a whole.

Oceanic basalts are formed by melting of a chemically and isotopically heterogeneous mantle source. The oceanic mantle probably resembles a marble cake containing layers of mafic rock-perhaps recycled ocean crust-stored in the mantle for >1 billion years. Many questions about the nature and distribution of these mantle heterogeneities remain. Here we show that lithological and isotopic traces of ancient mafic layers can still be seen in mantle rocks that have melted to form oceanic crust at a spreading centre in the Tethys Ocean. We have found centimetre-scale heterogeneity in initial osmium isotope ratios in mantle rocks from the Pindos Ophiolite. Deformed pyroxenite layers have high 187 Os/ 188 Os ratios (0.14-0.20) compared to adjacent host peridotites (187 Os/ 188 Os: 0.12-0.13). These layers were formed by a reaction between mantle rock and melt derived from ancient rocks with high Re/Os ratios. We interpret the pyroxenite layers as the wall rocks of billion-year old mafic layers that melted and transformed mantle peridotite into pyroxenite by melt-rock reaction. The pyroxenite layers are the melting residue of ancient metre-scale basaltic veins in a kilometre-sized marble cake domain in the oceanic mantle that has withstood homogenization on a billionyear time scale.

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Km and Vmax values for d(pT8) and its derivatives containing various 5'-end groups were estimated in the reaction of DNA polymerization alpha catalyzed by DNA polymerase alpha and HIV-RT. The effect of 5'-end modification of primer is more pronounced in the case of HIV-RT. Strong influence is observed for an intercalating (ethidium) group. The affinity of EtpT8 is 200-fold higher than that of d(pT8). Attachment of Phn-, Dnm- and Hem-groups results in the increase of affinity of modified primer from 10 up to 20 times. For DNA polymerase alpha the influence of modifiers on primer affinity is much weaker. The effect of 5'-end residues on the Vmax values is also more pronounced for HIV RT. The way to improve selective interaction of oligonucleotide derivatives with the primer site of HIV RT is suggested.