A ribosome assembly factor Ebp2p, the yeast homolog of EBNA1-binding protein 2, is involved in the secretory response

We have found that Ebp2p is essential for maturation of 25S rRNA and assembly of 60S pre-ribosomal subunits in Saccharomyces cerevisiae. We obtained three temperature-sensitive ebp2 mutants by PCR. Polysome analysis revealed that the synthesis of 60S ribosomal subunits was compromised in each of the ebp2 mutants at the restrictive temperature. The ebp2 alleles affected the transcriptional repression of both rRNA and ribosomal protein genes due to a secretion block. Fluorescence microscopy showed that a secretion block led to condensation of nucleolar Ebp2p, whereas that was not the case with the ebp2 mutant. These results suggest that Ebp2p is implicated in the secretory response, including changes in nucleolar architecture.