Fanconi Anaemia (FA) is a rare inherited syndrome characterized by reduced fertility, congenital abnormalities, progressive bone marrow failure and highly elevated risk of haematological and squamous cell cancers.  FA is caused by a loss of the ability to repair DNA interstrand crosslink damage; there are 15 FANC genes (FANCA-FANCP) that comprise the FA pathway and mutations in any of these 15 genes results in FA.

FANCM is of particular interest because it has an intrinsic DNA-binding activity and, in a heterodimer with FAAP24, can bind stalled replication forks. FANCM:FAAP24 is thought to be the anchor that recruits a signaling and repair mechanism that includes the products of the other 14 FANC genes. These constitute a 7-protein ubiquitin ligase, the ubiquitination substrates and several proteins involved in homologous recombination repair.

We are investigating the interaction between FANCM and the FANCF component of the ubiquitin ligase complex via its MM1 domain. We identified potential Cyclin/CDK and Chk1 phosphorylation sites within the MM1 domain that could play a part in the regulation of this protein interaction.

We demonstrate that these sites are phosphorylated in vitro and in vivo. We also show that mutation of the phosphorylation sites resulted in decreased binding to FANCF and the FA ubiquitin ligase complex. We are testing these mutants in a FANCM complementation system to assess their function in modulating the activity of the FA ubiquitin ligase complex and sensitivity to interstrand-crosslinking agents. A model of the potential effects of phosphorylation on FANCM structure will also be presented. This work will determine how FANCM is regulated via phosphorylation by cell cycle and checkpoint kinases, and the impact this phosphorylation has on the FA repair pathway.