Investigation of the Physiological Role of Ssb1 using an in-vivo Targeted Mouse Model

Abstract

Single-stranded DNA binding proteins (SSBs) are critical for binding, protecting and sequestering single-stranded DNA intermediates during multiple cellular transactions, including DNA replication, repair and transcription. The canonical SSB in eukaryotes, Replication Protein A (RPA), is a heterotrimeric protein essential for numerous cellular processes, including DNA repair by homologous recombination (HR). Recently, Richard et al. (2008) identified a novel human SSB, designated human Single-Stranded DNA Binding protein 1 (hSSB1), critical to DNA repair and the maintenance of genomic stability. siRNA-mediated depletion of hSSB1 led to attenuation of ATM signalling in response to DNA damage by ionizing radiation (IR), impairment of DNA repair by HR, and overall genetic instability. Moreover, hSSB1 was subsequently shown to itself function in a heterotrimeric complex in a manner analogous to RPA, with Integrator complex subunit 3 (INTS3), and a small, uncharacterised acidic protein C9Orf80/MISE/SSBIP1. siRNA-mediated depletion of these components led to similar DNA damage-related phenotypes to what has been observed for hSSB1 depletion alone, suggesting that complex formation may be important for hSSB1 functioning. Moreover, hSSB2, a homolog of hSSB1, was shown to be able to form a similar complex with INTS3 and C9Orf80 in place of hSSB1, suggesting an element of functional redundancy in the roles of hSSB1 and hSSB2.