Expression and localization studies of hSDA, the human ortholog of the yeast SDA1 gene

The yeast SDA1 gene was reported to play a critical role in G(1) events and to be involved in 60S ribosome biogenesis. Although the basic cellular mechanisms appear conserved from yeast to man, the human genes may have more diversified functions. In this view we obtained the first experimental evidences about the human ortholog of the yeast SDA1, i.e., hSDA. The gene is localized at the chromosomal region 4q21 and encodes for a 627a.a. long protein highly homologous to the yeast Sda1. Subcellular localization experiments indicate that the human protein behaves similarly to nucleolar proteins involved in rRNA processing machinery but not in RNA PolI transcriptional events. hSda appears localized in the granular component of the nucleolus and in the nucleoplasm, which is consistent with a role in early-intermediate steps of ribosome biogenesis. hSDA appears preferentially expressed in fetal tissues, pinpointing its role during development. Different expression levels in different tumor cell lines might suggest that the gene is involved also in tumorigenesis. However our preliminary results indicate that hSDA does not behave like a proapoptotic gene and its involvement in tumorigenesis is still to be clarified.