The SH3 Domain of αII Spectrin Is a Target for the Fanconi Anemia Protein, FANCG

The structural protein nonerythroid alpha spectrin (alpha IISp) plays a role in the repair of DNA interstrand cross-links and is deficient in cells from patients with Fanconi anemia (FA), in which there is a defect in ability to repair such cross-links. We have proposed a model in which alpha IISp, whose stability is dependent on FA proteins, acts as a scaffold to aid in recruitment of repair proteins to sites of damage. In order to get a clearer understanding of the proposed. role of FA proteins in maintaining stability of alpha IISp, yeast two-hybrid analysis was carried out to determine whether FA proteins directly interact with alpha IISp and, if so, to map the sites of interaction. Four overlapping regions of wwwctJlSp were constructed. FANCG interacted with one of these regions and specifically with the SH3 domain in this region of alpha IISp. The site of interaction in FANCG was mapped to a motif that binds to SH3 domains and contains a consensus sequence with preference for the SH3 domain of wwwallSp. This site of interaction was confirmed using site-directed mutagenesis. Two FA proteins that did not contain motifs that bind to SH3 domains, FANCC and FANCF, did not interact with the SH3 domain of wwwallSp. These results demonstrate that one of the FA proteins, FANCG, contains a motif that interacts directly with the SH3 domain of (wwwxIISp. We propose that this binding of FANCG to alpha IISp may be important for the stability of alpha IISp in cells and the role wwwwallSp plays in the DNA repair process.