Dual Requirement for Yeast hnRNP Nab2p in mRNA poly(A) Tail Length Control and Nuclear Export

Recent studies of mRNA export factors have provided additional evidence for a mechanistic link between mRNA 3′‐end formation and nuclear export. Here, we identify Nab2p as a nuclear poly(A)‐binding protein required for both poly(A) tail length control and nuclear export of mRNA. Loss of NAB2 expression leads to hyperadenylation and nuclear accumulation of poly(A)+ RNA but, in contrast to mRNA export mutants, these defects can be uncoupled in a nab2 mutant strain. Previous studies have implicated the cytoplasmic poly(A) tail‐binding protein Pab1p in poly(A) tail length control during polyadenylation. Although cells are viable in the absence of NAB2 expression when PAB1 is overexpressed, Pab1p fails to resolve the nab2Δ hyperadenylation defect even when Pab1p is tagged with a nuclear localization sequence and targeted to the nucleus. These results indicate that Nab2p is essential for poly(A) tail length control in vivo, and we demonstrate that Nab2p activates polyadenylation, while inhibiting hyperadenylation, in the absence of Pab1p in vitro. We propose that Nab2p provides an important link between the termination of mRNA polyadenylation and nuclear export

Reconstructing seasonality through stable-isotope and trace-element analyses of the Proserpine stalagmite, Han-sur-Lesse cave, Belgium : indications for climate-driven changes during the last 400 years

Fast-growing speleothems allow for the reconstruction of palaeoclimate down to a seasonal scale. Additionally, annual lamination in some of these speleothems yields highly accurate age models for these palaeoclimate records, making these speleothems valuable archives for terrestrial climate. In this study, an annually laminated stalagmite from the Han-sur-Lesse cave (Belgium) is used to study the expression of the seasonal cycle in northwestern Europe during the Little Ice Age. More specifically, two historical 12-year-long growth periods (ca. 1593-1605 CE and 1635-1646 CE) and one modern growth period (1960-2010 CE) are analysed on a sub-annual scale for their stable-isotope ratios (delta C-13 and delta O-18) and trace-element (Mg, Sr, Ba, Zn, Y, Pb, U) contents. Seasonal variability in these proxies is confirmed with frequency analysis. Zn, Y and Pb show distinct annual peaks in all three investigated periods related to annual flushing of the soil during winter. A strong seasonal in-phase relationship between Mg, Sr and Ba in the modern growth period reflects a substantial influence of enhanced prior calcite precipitation (PCP). In particular, PCP occurs during summers when recharge of the epikarst is low. This is also evidenced by earlier observations of increased delta C-13 values during summer. In the 17th century intervals, there is a distinct antiphase relationship between Mg, Sr and Ba, suggesting that processes other than PCP, i.e. varying degrees of incongruent dissolution of dolomite, eventually related to changes in soil activity and/or land-use change are more dominant. The processes controlling seasonal variations in Mg, Sr and Ba in the speleothem appear to change between the 17th century and 1960-2010 CE. The Zn, Y, Pb, and U concentration profiles; stable-isotope ratios; and morphology of the speleothem laminae all point towards increased seasonal amplitude in cave hydrology. Higher seasonal peaks in soil-derived elements (e.g. Zn and Y) and lower concentrations of host-rock-derived elements (e.g. Mg, Sr, Ba) point towards lower residence times in the epikarst and higher flushing rates during the 17th century. These observations reflect an increase in water excess above the cave and recharge of the epikarst, due to a combination of lower summer temperatures and increased winter precipitation during the 17th century. This study indicates that the transfer function controlling Mg, Sr and Ba seasonal variability varies over time. Which process is dominant - either PCP, soil activity or dolomite dissolution - is clearly climate driven and can itself be used as a palaeoenvironment proxy

Quasi-exactly solvable quartic potential

A new two-parameter family of quasi-exactly solvable quartic polynomial potentials $V(x)=-x^4+2iax^3+(a^2-2b)x^2+2i(ab-J)x$ is introduced. Until now, it was believed that the lowest-degree one-dimensional quasi-exactly solvable polynomial potential is sextic. This belief is based on the assumption that the Hamiltonian must be Hermitian. However, it has recently been discovered that there are huge classes of non-Hermitian, ${\cal PT}$-symmetric Hamiltonians whose spectra are real, discrete, and bounded below [physics/9712001]. Replacing Hermiticity by the weaker condition of ${\cal PT}$ symmetry allows for new kinds of quasi-exactly solvable theories. The spectra of this family of quartic potentials discussed here are also real, discrete, and bounded below, and the quasi-exact portion of the spectra consists of the lowest $J$ eigenvalues. These eigenvalues are the roots of a $J$th-degree polynomial.Comment: 3 Pages, RevTex, 1 Figure, encapsulated postscrip

Coupled Mg/Ca and clumped isotope analyses of foraminifera provide consistent water temperatures

The reliable determination of past seawater temperature is fundamental to paleoclimate studies. We test the robustness of two paleotemperature proxies by combining Mg/Ca and clumped isotopes (Δ47) on the same specimens of core top planktonic foraminifera. The strength of this approach is that Mg/Ca and Δ47 are measured on the same specimens of foraminifera, thereby providing two independent estimates of temperature. This replication constitutes a rigorous test of individual methods with the advantage that the same approach can be applied to fossil specimens. Aliquots for Mg/Ca and clumped analyses are treated in the same manner following a modified cleaning procedure of foraminifera for trace element and isotopic analyses. We analysed eight species of planktonic foraminifera from coretop samples over a wide range of temperatures from 2 to 29°C. We provide a new clumped isotope temperature calibrations using subaqueous cave carbonates, which is consistent with recent studies. Tandem Mg/Ca–Δ47 results follow an exponential curve as predicted by temperature calibration equations. Observed deviations from the predicted Mg/Ca-Δ47 relationship are attributed to the effects of Fe-Mn oxide coatings, contamination, or dissolution of foraminiferal tests. This coupled approach provides a high degree of confidence in temperature estimates when Mg/Ca and Δ47 yield concordant results, and can be used to infer the past δ18O of seawater (δ18Osw) for paleoclimate studies

Quotient Categories and Phases

We study properties of a category after quotienting out a suitable chosen group of isomorphisms on each object. Coproducts in the original category are described in its quotient by our new weaker notion of a 'phased coproduct'. We examine these and show that any suitable category with them arises as such a quotient of a category with coproducts. Motivation comes from projective geometry, and also quantum theory where they describe superpositions in the category of Hilbert spaces and continuous linear maps up to global phase. The quotients we consider also generalise those induced by categorical isotropy in the sense of Funk et al.Comment: Fixed typos, added discussion of isotropy, expanded introductio

Spin Structures on Kleinian Manifolds

We derive the topological obstruction to spin-Klein cobordism. This result has implications for signature change in general relativity, and for the $N=2$ superstring.Comment: 8 page