Utp14 recruits and activates the RNA helicase Dhr1 to undock U3 snoRNA from the pre-ribosome

Abstract

In eukaryotic ribosome biogenesis, U3 snoRNA base-pairs with the pre-rRNA to promote its processing. However, U3 must be removed to allow folding of the central pseudoknot, a key feature of the small subunit. Previously, my work contributed to showing that the DEAH/RHA RNA helicase Dhr1 dislodges U3 from the pre-rRNA. DHR1 can be linked to UTP14, encoding an essential protein of the pre-ribosome, through genetic interactions with the rRNA methyltransferase Bud23. Here, I report that Utp14 regulates Dhr1. Mutations within a discrete region of Utp14 reduced its interaction with Dhr1 that correlated with reduced function of Utp14. These mutants accumulated Dhr1 and U3 in a pre-40S particle, mimicking a helicase inactive Dhr1 mutant. This similarity in the phenotypes led us to propose that Utp14 activates Dhr1. Indeed, Utp14 formed a complex with Dhr1 and stimulated its unwinding activity in vitro. Moreover, the utp14 mutants that mimicked a catalytically inactive dhr1 mutant in vivo showed reduced stimulation of unwinding activity in vitro. Dhr1 binding to the pre-ribosome was substantially reduced only when both Utp14 and Bud23 are depleted. Thus, Utp14 is bifunctional; together with Bud23 it is needed for stable interaction of Dhr1 with the pre-ribosome and Utp14 activates Dhr1 to dislodge U3.