Identification of an evolutionary conserved SURF-6 domain in a family of nucleolar proteins extending from human to yeast.

The mammalian SURF-6 protein is localized in the nucleolus, yet its function remains elusive in the recently characterized nucleolar proteome. We discovered by searching the Protein families database that a unique evolutionary conserved SURF-6 domain is present in the carboxy-terminal of a novel family of eukaryotic proteins extending from human to yeast. By using the enhanced green fluorescent protein as a fusion protein marker in mammalian cells, we show that proteins from distantly related taxonomic groups containing the SURF-6 domain are localized in the nucleolus. Deletion sequence analysis shows that multiple regions of the SURF-6 protein are capable of nucleolar targeting independently of the evolutionary conserved domain. We identified that the Saccharomyces cerevisiae member of the SURF-6 family, named rrp14 or ykl082c, has been categorized in yeast databases to interact with proteins involved in ribosomal biogenesis and cell polarity. These results classify SURF-6 as a new family of nucleolar proteins in the eukaryotic kingdom and point out that SURF-6 has a distinct domain within the known nucleolar proteome that may mediate complex protein-protein interactions for analogous processes between yeast and mammalian cells.