Crises and Rating Agencies

We analyze a rating agency's incentives to distort ratings in a model with a monopolistic profit maximizing rating agency, a continuum of heterogeneous firms, and a competitive market of risk-neutral investors. Firms sell bonds, the value of a firm's bond is known to the firm and observable by the agency, but not by buyers. Firms can choose to get a rating. The rating agency can reveal a signal of arbitrary precision about the quality of the bond. In contrast to the existing literature, we allow aggregate uncertainty. As in the existing literature, one rating class is optimal. However, the rating agency does not choose a socially optimal cutoff: the agency is more likely to be too lenient if the distribution of aggregate uncertainty has a lower mean, a higher variance, and is more left skewed. It is more likely to be too strict if the opposite holds

Essays in information economics and communication

Communication and Public Goods, Bayesian Persuasion with Private Experimentation, Crisis and Credit Rating Agencie

Surface Measure to Depth (SMeTD): a new low-budget system for 3D water temperature measurements for combining with UAV-based thermal infrared imagery

Acknowledgements This work was funded by the School of Geosciences, University of Aberdeen, and the Macaulay Development Trust. We would like to thank Dr. Katya Dimitrova Petrova, Dr. Irma Arts, Douglas Wardell-Johnson and Lucas Christie for their assistance in the field. Funding This work was funded by the School of Geosciences, University of Aberdeen, and the Macaulay Development Trust.Peer reviewedPublisher PD

Long-term daily stream temperature record for Scotland reveals spatio-temporal patterns in warming of rivers in the past and further warming in the future

Peer reviewedproo

Cargo and Dynamin Regulate Clathrin-Coated Pit Maturation

Total internal reflection fluorescence microscopy (TIR-FM) has become a powerful tool for studying clathrin-mediated endocytosis. However, due to difficulties in tracking and quantifying their heterogeneous dynamic behavior, detailed analyses have been restricted to a limited number of selected clathrin-coated pits (CCPs). To identify intermediates in the formation of clathrin-coated vesicles and factors that regulate progression through these stages, we used particle-tracking software and statistical methods to establish an unbiased and complete inventory of all visible CCP trajectories. We identified three dynamically distinct CCP subpopulations: two short-lived subpopulations corresponding to aborted intermediates, and one longer-lived productive subpopulation. In a manner dependent on AP2 adaptor complexes, increasing cargo concentration significantly enhances the maturation efficiency of productive CCPs, but has only minor effects on their lifetimes. In contrast, small interfering RNA (siRNA) depletion of dynamin-2 GTPase and reintroduction of wild-type or mutant dynamin-1 revealed dynamin's role in controlling the turnover of abortive intermediates and the rate of CCP maturation. From these data, we infer the existence of an endocytic restriction or checkpoint, responsive to cargo and regulated by dynamin

Structure of the mammalian ribosome as it decodes the selenocysteine UGA codon

The elongation of eukaryotic selenoproteins relies on a poorly understood process of interpreting in-frame UGA stop codons as selenocysteine (Sec). We used cryo-electron microscopy to visualize Sec UGA recoding in mammals. A complex between the noncoding Sec-insertion sequence (SECIS), SECIS-binding protein 2 (SBP2), and 40S ribosomal subunit enables Sec-specific elongation factor eEFSec to deliver Sec. eEFSec and SBP2 do not interact directly but rather deploy their carboxyl-terminal domains to engage with the opposite ends of the SECIS. By using its Lys-rich and carboxyl-terminal segments, the ribosomal protein eS31 simultaneously interacts with Sec-specific transfer RNA (tRNASec) and SBP2, which further stabilizes the assembly. eEFSec is indiscriminate toward l-serine and facilitates its misincorporation at Sec UGA codons. Our results support a fundamentally distinct mechanism of Sec UGA recoding in eukaryotes from that in bacteria

Structures of ribosome-bound initiation factor 2 reveal mechanism of subunit association

Throughout the four phases of protein biosynthesis—initiation, elongation, termination, and recycling—the ribosome is controlled and regulated by at least one specified translational guanosine triphosphatase (trGTPase). Although the structural basis for trGTPase interaction with the ribosome has been solved for the last three steps of translation, the high-resolution structure for the key initiation trGTPase, initiation factor 2 (IF2), complexed with the ribosome, remains elusive. We determine the structure of IF2 complexed with a nonhydrolyzable guanosine triphosphate analog and initiator fMet-tRNAiMet in the context of the Escherichia coli ribosome to 3.7-Å resolution using cryo-electron microscopy. The structural analysis reveals previously unseen intrinsic conformational modes of the 70S initiation complex, establishing the mutual interplay of IF2 and initator transfer RNA (tRNA) with the ribsosome and providing the structural foundation for a mechanistic understanding of the final steps of translation initiation