Zeyu Zhou

Conceptions of omissions standardly come in two flavours: omissions are construed either as mere absences of actions or are closely related to paradigmatic ‘positive’ actions. This paper shows how the semantics of the verb ‘to omit’ constitutes strong evidence against the view of omissions as involving actions. Specifically, by drawing from an influential fourfold typology of verbal predicates popularised by Zeno Vendler, I argue that declarative statements involving reference to omissions are semantically stative, which is a finding that makes serious trouble for the conception of omissions as being closely related to paradigmatic actions. But references to omissions, in certain linguistic contexts, undergo a shift of meaning to describe processes or activities engaged in by the agent. Still, despite the semantic flexibility of the verb ‘to omit’, its processive reading does not straightforwardly support the second conception of omissions. A subsidiary aim of this paper is to offer a sketch of the metaphysics of processive action in order to show what those who claim that omissions are closely related to actions might be committed to.

© 2016, American Society for Biochemistry and Molecular Biology Inc. All rights reserved.Glycyl-tRNA synthetase is the enzyme that covalently links glycine to cognate tRNA for translation. It is of great research interest because of its nonconserved quaternary structures, unique species-specific aminoacylation properties, and noncanonical functions in neurological diseases, but none of these is fully understood. We report two crystal structures of human GlyRS variants, in the free form and in complex with tRNAGly respectively, and reveal new aspects of the glycylation mechanism. We discover that insertion 3 differs considerably in conformation in catalysis and that it acts like a "switch" and fully opens to allow tRNA to bind in a cross-subunit fashion. The flexibility of the protein is supported by molecular dynamics simulation, as well as enzymatic activity assays. The biophysical and biochemical studies suggest that human GlyRS may utilize its flexibility for both the traditional function and alternative functions.