RESUMO
The ribosome small subunit (SSU) is assembled by the SSU processome which contains approximately 70 non-ribosomal protein factors. Whilst the biochemical mechanisms of the SSU processome in 18S rRNA processing and maturation have been extensively studied, how SSU processome components enter the nucleolus has yet to be systematically investigated. Here, in examining the nucleolar localization of 50 human SSU processome components, we found that UTP3, together with another 24 proteins, enter the nucleolus autonomously. For the remaining 25 proteins we found that UTP3/SAS10 assists the nucleolar localization of five proteins (MPP10, UTP25, EMG1 and the two UTP-B components UTP12 and UTP13), likely through its interaction with nuclear importin α. This 'ferrying' function of UTP3 was then confirmed as conserved in the zebrafish. We also found that knockdown of human UTP3 impairs cleavage at the A0-site while loss-of-function of either utp3/sas10 or utp13/tbl3 in zebrafish causes the accumulation of aberrantly processed 5'ETS products, which highlights the crucial role of UTP3 in mediating 5'ETS processing. Mechanistically, we found that UTP3 facilitates the degradation of processed 5'ETS by recruiting the RNA exosome component EXOSC10 to the nucleolus. These findings lay the groundwork for studying the mechanism of cytoplasm-to-nucleolus trafficking of SSU processome components.
RESUMO
Dnttip2 is one of the components of the small subunit (SSU) processome. In yeast, depletion of dnttip2 leads to an inefficient processing of pre-rRNA and a decrease in synthesis of the mature 18S rRNA. However, the biological roles of Dnttip2 in higher organisms are poorly defined. In this study, we demonstrate that dnttip2 is a maternal gene in zebrafish. Depletion of Dnttip2 leads to embryonic lethal with severe digestive organs hypoplasia. The loss of function of Dnttip2 also leads to partial defects in cleavage at the A0-site and E-site during 18S rRNA processing. In conclusion, Dnttip2 is essential for 18S rRNA processing and digestive organ development in zebrafish.