Expression and characterization of the human rps3 in a methylotrophic yeast Pichia pastoris

A human ribosomal protein S3 (rpS3), which also functions as a DNA repair enzyme (UV endonuclease III), was expressed in a methylotrophic yeast, Pichia pastoris, and biochemically characterized. UV endonuclease activity was previously characterized, and this activity of mammalian rpS3 was found to be non-specific upon purification and storage. Under the Pichia expression system, the subcloned cDNA of the human rpS3 gene revealed a peptide of 42 kDa by SDS-PAGE and Western blot. The secreted form of human rpS3 rendered no endonuclease activity while the intracellular form showed UV specific endonuclease activity by the nick circle assay.