New Roles for RACK1 in Translational Control
RACK1 is a highly conserved scaffold protein that acts on the ribosome to regulate translation and signaling. Prior studies have largely considered the ribosomal and extraribosomal functions of RACK1 to be separate and unrelated. Gallo et al. (e00230-18) now show that these two aspects of RACK1 are in fact intimately connected and influence each other. On ribosomes, RACK1 specifically promotes cap-dependent translation and recruits eukaryotic initiation factor 4E to mRNAs. Off of ribosomes, RACK1 inhibits translation, possibly by activating stress signaling. RACK1 thus acts as a link between the translation machinery and signaling, with its function dependent on ribosomal association.
Activation of Budding Yeast Kin1/2 Kinases by Transphosphorylation of the Activation Loop
The unfolded protein response (UPR) is a mechanism that cells trigger to alleviate the stress caused by the accumulation of unfolded proteins in the endoplasmic reticulum (ER). Prior studies have shown that the budding yeast protein kinases Kin1 and Kin2 (orthologs of microtubule affinity-regulating kinase in humans) contribute to UPR function. The Kin kinases contain a conserved kinase domain and an autoinhibitory kinase-associated 1 (KA1) domain separated by a long undefined domain. Ghosh et al. (e00266-18) show that during ER stress the Kin kinase domain is released from its autoinhibitory KA1 domain and is activated by transphosphorylation.
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