DBP7P, A PUTATIVE ATP-DEPENDENT RNA HELICASE FROM SACCHAROMYCES-CEREVISIAE, IS REQUIRED FOR 60S RIBOSOMAL-SUBUNIT ASSEMBLY

Putative ATP-dependent RNA helicases are ubiquitous, highly conserved proteins that are found in most organisms and they are implicated in a ll aspects of cellular RNA metabolism. Here we present the functional characterization of the Dbp7 protein, a putative ATP-dependent RNA hel icase of the DEAD-box protein family from Saccharomyces cerevisiae. Th e complete deletion of the DBP7ORF causes a severe slow-growth phenoty pe. In addition, the absence of Dbp7p results in a reduced amount of 6 0S ribosomal subunits and an accumulation of halfmer polysomes. Subseq uent analysis of pre-rRNA processing indicates that this 60S ribosomal subunit deficit is due to a strong decrease in the production of 27S and 7S precursor rRNAs, which leads to reduced levels of the mature 25 S and 5.8S rRNAs. Noticeably, the overall decrease of the 27S pre-rRNA species is neither associated with the accumulation of preceding prec ursors nor with the emergence of abnormal processing intermediates, su ggesting that these 27S pre-rRNA species are degraded rapidly in the a bsence of Dbp7p. Finally, an HA epitope-tagged Dbp7 protein is localiz ed in the nucleolus. We propose that Dbp7p is involved in the assembly of the pre-ribosomal particle during the biogenesis of the 60S riboso mal subunit.