Diauxic shift-dependent relocalization of decapping activators Dhh1 and Pat1 to polysomal complexes

Drummond, Sheona P.; Hildyard, John; Firczuk, Helena; Reamtong, Onrapak; Li, Ning; Kannambath, Shichina; Claydon, Amy J.; Beynon, Robert J.; Eyers, Claire E.; McCarthy, John E. G.

In this study, we examine the undefined relationship between Dhh1/Pat1 and the translation machinery. We focus on their respective cellular distributions, since these are directly relevant to the functions of these proteins. For example, if the spatial distributions of a regulatory molecule and its target do not overlap, this exercises a limiting effect on the regulatory competence of the regulator. Imaging of fluorescently tagged cellular components, combined with analyses of the composition of polysomal complexes, reveals a remarkable degree of separation of these proteins from ribosomal populations during exponential cell growth, i.e. in cells lacking P bodies. This is found to correlate with spatial segregation of these proteins from actively translating polysomal complexes. In contrast, Dhh1 and Pat1 gain greatly increased access to actively translating polysomes in the phase of growth that is associated with the shift from glucose fermentation to ethanol oxidation (the diauxic growth shift). This has prompted us to investigate whether there is a control relationship between translation rate and these relocation events, and to characterize protein interactions involving Dhh1 and the translation machinery that are likely to be relevant to the functional roles of these decapping modulators in the cell. The results suggest that segregation of Dhh1 and Pat1 from actively translating polysomes, like the formation of P bodies, reflects modulation of the access of these translational repressors to the translational machinery. Thus modulation of the subcellular localization of translational effectors may play a role in post-transcriptional control.