Abstract
DEAD-box RNA helicases play important roles in a wide range of metabolic processes. Regulatory proteins can stimulate or block the activity of DEAD-box helicases. Here, we show that LOTUS (Limkain, Oskar, and Tudor containing proteins 5 and 7) domains present in the germline proteins Oskar, TDRD5 (Tudor domain-containing 5), and TDRD7 bind and stimulate the germline-specific DEAD-box RNA helicase Vasa. Our crystal structure of the LOTUS domain of Oskar in complex with the C-terminal RecA-like domain of Vasa reveals that the LOTUS domain occupies a surface on a DEAD-box helicase not implicated previously in the regulation of the enzyme's activity. We show that, in vivo, the localization of Drosophila Vasa to the nuage and germ plasm depends on its interaction with LOTUS domain proteins. The binding and stimulation of Vasa DEAD-box helicases by LOTUS domains are widely conserved.
Highlights
RNA helicases are key enzymes involved in almost all RNA metabolic processes, such as RNA synthesis, processing, translation, and decay (Linder and Jankowsky 2011)
The LOTUS domain is present in the germline proteins Tudor domain containing 5 (TDRD5), TDRD7, and meiosis arrest female 1 (MARF1) (Fig. 1A)
In contrast to Oskar and MARF1, GFP fusions to the Drosophila TDRD5 and TDRD7 orthologs Tejas and Tapas localized to the cytoplasm of S2R+ cells either uniformly (Tejas) or in speckles (Tapas)
Summary
RNA helicases are key enzymes involved in almost all RNA metabolic processes, such as RNA synthesis, processing, translation, and decay (Linder and Jankowsky 2011). The conserved DEAD-box RNA helicase Vasa plays diverse functions in germ cell formation and germline maintenance in animals (Raz 2000; Lasko 2013). Like Oskar, the proteins TDRD5, TDRD7, and MARF1 play critical roles in germ cell development in animals, but their molecular function is not known. Tejas and Tapas interact with Vasa in coimmunoprecipitation experiments, and, in the case of Tejas, the LOTUS domain is required for the interaction (Patil and Kai 2010; Patil et al 2014) This observation, together with our finding that the Oskar LOTUS domain interacts with Vasa but not RNA (Jeske et al 2015), raised the question of whether Vasa interaction might be a conserved function of LOTUS domains. Our analysis identified the eLOTUS domain as a novel DEAD-box RNA helicase regulator and sheds light on the function of LOTUS domain proteins in animals
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