Identification and Characterization of a Novel Sirtuin-like Nuclease, FLJ20635

Abstract

SIR2 proteins, otherwise known as sirtuins, are evolutionarily conserved throughout archaea, bacteria and eukaryotes, and are well known to be Class III NAD+-dependent histone deacetylases. Although early SIR2 proteins have been shown to play pivotal roles in mating type interconversion and transcriptional silencing, members of the sirtuin family have been extensively studied as potential anti-aging factors in the later years. Sirtuins act as key homeostatic regulators to ameliorate various aspects of aging, which is essentially an accumulation of genetic damages. Genomic stability and epigenetic alterations by sirtuins are important to prevent the accumulation of such genetic damages. Efficient DNA repair systems must be employed to ensure genomic stability. Although sirtuins have been implicated in DNA repair, there is no existing evidence that sirtuins could bind to and directly interact with DNA to aid in DNA repair. In this study, we have discovered a novel sirtuin-like nuclease, FLJ20635/FAM118A, which we have renamed as SIRTN. SIRTN contains a conserved SIR2-like domain, shares some level of conservation with other sirtuins and interestingly possesses nuclease activity. The nuclease activity has also been found to be present in SIRT2. Although preliminary, this represents a founding study indicating that sirtuins could play direct roles in DNA via the nuclease cleavage of DNA. The nuclease activity of SIRTN is found to be manganese-dependent, time-dependent and concentration-dependent. In particular, SIRTN is shown to be a 3’ to 5’ exonuclease while possessing some endonuclease activity as well. Interestingly, results from this study also suggest that the nuclease activity of SIRTN could be more important than its NAD+-dependent histone deacetylase activity.