HUMAN HELICASE GENE SKI2W IN THE HLA CLASS-III REGION EXHIBITS STRIKING STRUCTURAL SIMILARITIES TO THE YEAST ANTIVIRAL GENE SKI2 AND TO THE HUMAN GENE KIAA0052 - EMERGENCE OF A NEW GENE FAMILY

Helicases are essential enzymes for life because DNA replication, DNA repair recombination, transcription, RNA splicing and translation all involve more than one helicase to unwind DNA or RNA. We have discovered, cloned and partially characterized a novel human helicase gene, SKI2W. The human SKI2W is located between the RD and RP1 genes in the class III region of the major histocompatibility complex (MHC) on chromosome 6, a genomic region associated with many malignant, genetic and autoimmune diseases. Derived amino acid sequence of human SKI2W showed an open reading frame for 1246 residues. It contains consensus sequences for structural motifs of an RNA helicase with a DEVH box. It has a leucine zipper motif that may be important for protein dimerization, and an RGD motif close to the N-terminus that might serve as a ligand for integrin or cell adhesion molecules. SKI2W shares a striking and extensive similarity to the yeast Ski2p that is involved in the inhibition of translation of poly(A) negative [poly(A)-] RNA, and plays an important role in antiviral activities. Human SKI2W fusion protein expressed in insect cells using a baculovirus vector has ATPase activity. The human SKI2W protein and the yeast Ski2p share extensive sequence similarities to another putative human protein KIAA0052, suggesting the presence of a new gene family that may be involved in translational regulation of cellular and viral RNA.