Sr and Pb isotopic composition of five USGS glasses (BHVO-2G, BIR-1G, BCR-2G, TB-1G, NKT-1G)

Sr isotopic compositions and Rb/Sr ratios of three USGS glasses (BHVO-2G, BIR-1G, BCR-2G) are identical to those of the original USGS reference materials. NKT-1G and TB-1G give values of 0.70351 and 0.70558, respectively. Pb isotopic ratios were measured by the standard-sample bracketing technique on an MC-ICP-MS, which give results that are comparable in accuracy and reproducibility to double spike analyses. However, assessment of the reproducibility of the technique is hampered by inhomogeneous contamination of all USGS reference materials analysed. This contamination is likely to be the reason why the USGS glasses do not all have the same Pb isotopic composition as their unfused originals. Powdered glasses, distributed for characterisation of the glasses by bulk analytical techniques, do not all have the same Pb isotopic compositions as the solid glass material, and can therefore not be used for this purpose. © 2005 Elsevier B.V. All rights reserved

Retrotransposons. An RNA polymerase III subunit determines sites of retrotransposon integration.

International audienceMobile genetic elements are ubiquitous. Their integration site influences genome stability and gene expression. The Ty1 retrotransposon of the yeast Saccharomyces cerevisiae integrates upstream of RNA polymerase III (Pol III)-transcribed genes, yet the primary determinant of target specificity has remained elusive. Here we describe an interaction between Ty1 integrase and the AC40 subunit of Pol III and demonstrate that AC40 is the predominant determinant targeting Ty1 integration upstream of Pol III-transcribed genes. Lack of an integrase-AC40 interaction dramatically alters target site choice, leading to a redistribution of Ty1 insertions in the genome, mainly to chromosome ends. The mechanism of target specificity allows Ty1 to proliferate and yet minimizes genetic damage to its host