Counting target molecules by exponential polymerase chain reaction: copy number of mitochondrial DNA in rat tissues

In this report, we show that the actual number of target molecules of the polymerase chain reaction can be determined by measuring the concentration of product accumulating in consecutive cycles. The equation describing product accumulation, log Nn = log eff x n + log N0, can be analyzed by linear regression and the molar concentration of target at cycle zero, N0, is obtained. Using this new approach, the actual content of mitochondrial DNA was determined in rat tissues and ranged from 116 x 10(9) molecules/g in fast-twitch skeletal muscle to 743 x 10(9) molecules/g in liver. Using morphometric data from the literature, mitochondria were found to contain 1 to 3 DNA molecules. There was no relation between the oxidative capacity of a tissue and its content of mitochondrial DNA, indicating that transcriptional and posttranscriptional mechanisms rather than gene dosage, as postulated by others, determine to what extent the mitochondrial genome is expressed

Confirmation of Arabia plate slow motion by new GPS data in Yemen

During the last 10 years, a network of about 30 GPS sites was measured in Djibouti, East Africa. Additional points were also measured in Yemen, Oman, Ethiopia, Iran, and on La Réunion island. Merged with data from the available International GPS Service permanent stations scattered on the different plates in the area (Eurasia, Anatolia, Africa, Arabia, Somalia), this unique data set provides new insight on the current deformation in the Africa-Somalia-Arabia triple junction area and on the Arabian plate motion. Here we show that coherent motions of points in Yemen, Bahrain, Oman, and Iran allow us to estimate a geodetically constrained angular velocity for the Arabian plate (52.59°N, 15.74°W, 0.461°/Myr in ITRF2000). This result differs significantly from earlier determinations and is based upon our vectors in Yemen. They provide new additional data and better geometry for angular velocity determination. Combined with the African and Somalian motions, this new angular velocity results in predicted spreading rates in the Red Sea and the Gulf of Aden which are 15-20% lower than those measured from oceanic magnetic anomalies and thus averaged over the last 3 Myr. With respect to Eurasia, the geodetic motion of Arabia is also about 30% slower than predicted by NUVEL-1A. On the basis of the kinematic results presented here and on other evidence for a similar slower geodetic rate of the Indian plate, we suggest that the whole collision zone between Africa, Arabia, India on one hand and Eurasia on the other hand has slowed down in the last 3 Myr

Interseismic strain accumulation measured by GPS in the seismic gap between Constitución and Concepción in Chile

International audienceThe Concepción-Constitución area [35-37°S] in South Central Chile is very likely a mature seismic gap, since no large subduction earthquake has occurred there since 1835. Three campaigns of Global Positioning System (GPS) measurements were carried out in this area in 1996, 1999 and 2002. We observed a network of about 40 sites, including two East-West transects ranging from the coastal area to the Argentina border and one North-South profile along the coast. Our measurements are consistent with the Nazca/South America relative angular velocity (55. 9°N, 95.2°W, 0.610 °/ Ma) discussed by Vigny et al., 2008 (this issue) which predicts a convergence of 68mm/yr oriented 79°N at the Chilean trench near 36°S. With respect to stable South America, horizontal velocities decrease from 45mm/yr on the coast to 10mm/yr in the Cordillera. Vertical velocities exhibit a coherent pattern with negative values of about 10mm/yr on the coast and slightly positive or near zero in the Central Valley or the Cordillera. Horizontal velocities have formal uncertainties in the range of 1-3mm/yr and vertical velocities around 3 to 6mm/yr. Surface deformation in this area of South Central Chile is consistent with a fully coupled elastic loading on the subduction interface at depth. The best fit to our data is obtained with a dip of 16° +/- 3°, a locking depth of 55 +/- 5km and a dislocation corresponding to 67mm/yr oriented N78°. However in the Northern area of our network the fit is improved locally by using a lower dip around 13°. Finally a convergence motion of about 68mm/yr represents more than 10 m of displacement accumulated since the last big interplate subduction event in this area over 170 years ago (1835 earthquake described by Darwin). Therefore, in a worst case scenario, the area already has a potential for an earthquake of magnitude as large as 8 to 8.5, should it happen in the near future

The Mw=8.1 Antofagasta (North Chile) earthquake of july 30, 1995 : first results from teleseismic and geodetic data

A strong (Mw = 8.1) subduction earthquake occurred on July 30, 1995 in Antofagasta (northern Chile). This is one of the largest events during this century in the region. It ruptured the southernmost portion of a seismic gap between 18°S and 25°S. In 1992 we had used GPS to survey a network with about 50 benchmarks covering a region nearly 500 km long (N-S) and 200 km wide (E-W). Part of these marks were re-surveyed with GPS after the 1995 earthquake. Comparison towards the trench reaching 0.7 m. The inland subsided several decimeters. The Mejillones Peninsula was uplifted by more than 15 cm. Teleseismic body-wave modelling of VBB records gives a subduction focal mechanism and source time function with three distinct episodes of moment release and southward directivity. Modelling the displacement field using a dislocation with uniform slip in elastic half-space suggests a rupture zone with 19°-24° eastward dip extending to a depth no greater than 50 km with N-S length of 180 km and an average slip of about 5 m. The component of right-lateral slip inferred both from the teleseismic and geodetic data does not require slip partitioning at the plate boundary. That the well-constrained northern end of the 1995 rupture zone lies under the southern part of the Mejillones Peninsula increases the probability for a next rupture in the gap north of it. (Résumé d'auteur