Pr2_2Ir2_2O7_7: when Luttinger semimetal meets Melko-Hertog-Gingras spin ice state

We study the band structure topology and engineering from the interplay between local moments and itinerant electrons in the context of pyrochlore iridates. For the metallic iridate Pr$_2$Ir$_2$O$_7$, the Ir $5d$ conduction electrons interact with the Pr $4f$ local moments via the $f$-$d$ exchange. While the Ir electrons form a Luttinger semimetal, the Pr moments can be tuned into an ordered spin ice with a finite ordering wavevector, dubbed "Melko-Hertog-Gingras" state, by varying Ir and O contents. We point out that the ordered spin ice of the Pr local moments generates an internal magnetic field that reconstructs the band structure of the Luttinger semimetal. Besides the broad existence of Weyl nodes, we predict that the magnetic translation of the "Melko-Hertog-Gingras" state for the Pr moments protects the Dirac band touching at certain time reversal invariant momenta for the Ir conduction electrons. We propose the magnetic fields to control the Pr magnetic structure and thereby indirectly influence the topological and other properties of the Ir electrons. Our prediction may be immediately tested in the ordered Pr$_2$Ir$_2$O$_7$ samples. We expect our work to stimulate a detailed examination of the band structure, magneto-transport, and other properties of Pr$_2$Ir$_2$O$_7$.Comment: 10 pages, 7 figures, added more ref

Analysis of the role of poly(A) -binding protein (PAB1) in the mRNA degradation process in yeast

The mRNA deadenylation process influences multiple aspects of protein synthesis and is known to be the major factor controlling mRNA decay rates. My data demonstrates that yeast PAB1 plays both positive and negative roles in controlling deadenylation, and I have identified particular regions of PAB1 involved in controlling different aspects of the mRNA degradative process. I have found that yeast PAB1 does not play a simple, obstructionist role in regulating CCR4 deadenylation. Instead, PAB1-PAB1 protein interactions, as mediated by the PAB1 proline-rich region (P domain) and the RRM1 domain, are required for the CCR4 deadenylase activity. The P and RRM1 domains were shown to mediate PAB1-PAB1 binding, suggesting that enhancing CCR4 function entails the rearrangement of the PAB1-mRNP structure. I have also established that PAB1 contacts to the poly (A) tail made by the RRM2 domain are critical to stabilizing the CCR4-NOT complex and promoting deadenylation. The C-terminal globular domain of PAB1 through its contacts to eRF3 is also required for CCR4 deadenylation. In contrast, the RRM3 domain of PAB1 inhibits deadenylation and decapping. mRNP structures involving the terminal PAB1 bound to poly (A) are also affected by RRM3 and control the end to deadenylation and apparently the commencement of decapping. These results indicate that PAB1 integrates and controls the transition from deadenylation to decapping and from a translationally competent state to an mRNA degradative state