Speaker: David Somers, Professor in the Department of Molecular Genetics at The Ohio State University

Title: "Post-translational mechanisms of circadian regulation"

Abstract: The bases of the circadian oscillator are autoregulatory negative feedback loops involving transcriptional, post-transcriptional and post-translational mechanisms. While much early research focused on identifying transcriptional control factors, increasingly post-transcriptional and post-translational processes are emerging as essential to the normal operation of circadian systems.

Nucleocytoplasmic shuttling is essential for proper clock function although few components of the nuclear pore (NP) have been implicated as regulatory in any circadian system. We have identified mutations in NP components in Arabidopsis that lengthen circadian period and are associated with mRNA export defects and misregulated protein SUMOylation. NUCLEAR PORE ANCHOR (NUA), with similarity to the inner nuclear basket proteins Tpr (Translocated Promoter Region), Mlp1/Mlp2 (Myosin-like proteins 1 and 2), and Megator is located at the inner nuclear envelope within the “nuclear basket” of the NP. Circadian period is lengthened in nua mutants by 1-2 hours. nua mutants exhibit high accumulation of SUMO conjugates, but epistasis tests with the SUMO ligase mutant (siz1) indicate that the role of NUA in the circadian system is likely not due to SUMO-dependent effects on the clock.

Strikingly, double mutants between nua and select clock mutants point to the core clock component, TOC1, as a key element affected by NUA loss. Nuclear/cytoplasmic fractionation and confocal microscopy show higher nuclear levels of TOC1 in the nua mutant, consistent with the longer period. These and other data will be presented to show that one role for NUA in the circadian system is in the regulation of the nucleocytoplasmic partitioning of select clock proteins.

Host: Steve Howell, Distinguished Professor

Please join us for refreshments before the seminar outside Room 1414 of the Molecular Biology Building.