SMAD7 binds to SMURF1 in the nucleus (Ebisawa et al. 2001, Tajima et al. 2003). SMURF1 domains WW1 and WW2, highly similar to WW2 and WW3 domains of SMURF2, are involved in SMAD7 binding. SMURF1 has two splicing isoforms. The shorter splicing isoform of SMURF1 has an inter-WW domain linker of the same length as the WW2-WW3 domain linker of SMURF2. The longer isoform of SMURF1 has a longer WW1-WW2 domain linker, resulting in decreased affinity of the longer SMURF1 isoform for SMAD7 (Chong et al. 2010). This is based on experiments with recombinant mouse Smad7 and recombinant human SMURF1.