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J. Biol. Chem., Vol. 278, Issue 40, 38847-38859, October 3, 2003

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Down-regulation of RNA Helicase II/Gu Results in the Depletion of 18 and 28 S rRNAs in Xenopus Oocyte^*

Hushan Yang , Juhua Zhou , Robert L. Ochs , Dale Henning , Runyan Jin  and Benigno C. Valdez  ¶

From the Department of Pharmacology, Baylor College of Medicine, Houston, Texas 77030 and Precision Therapeutics, Inc., Pittsburgh, Pennsylvania 15203

Genetic manipulations have revealed the functions of RNA helicases in ribosomal RNA (rRNA) biogenesis in yeast. However, no report shows the role of an RNA helicase in rRNA formation in higher eukaryotes. This study reports the functional characterization of the frog homologue of nucleolar RNA helicase II/Gu (xGu or DDX21). Down-regulation of xGu in Xenopus laevis oocyte using an antisense oligodeoxynucleotide results in the depletion of 18 and 28 S rRNAs. The disappearance of 18 S rRNA is accompanied by an accumulation of 20 S, indicating that xGu is critical in the processing of 20 to 18 S rRNA. The degradation of 28 S rRNA into fragments smaller than 18 S is also associated with a specific decrease in the level of xGu protein. These effects are reversed in the presence of in vitro synthesized wild type xGu mRNA but not its helicase-deficient mutant form. Similar aberrant rRNA processing is observed when antibody against xGu is microinjected. The involvement of xGu in processing of rRNA is consistent with the localization of Gu protein to the granular and dense fibrillar components of PtK2 cell nucleoli by immunoelectron microscopy. Our results show that xGu is involved in the processing of 20 to 18 S rRNA and contributes to the stability of 28 S rRNA in Xenopus oocytes.

Received for publication, March 4, 2003 , and in revised form, July 7, 2003.

^* This work was supported by Public Health Service Grant DK52341 from the NIDDK, National Institutes of Health (to B. C. V.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

^¶ To whom correspondence should be addressed: Dept. of Pharmacology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030. Tel.: 713-798-7908; Fax: 713-798-3145; E-mail: bvaldez{at}bcm.tmc.edu.

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