Defining the heterochromatin localization and repression domains of SALL1.

SALL1 has been identified as one of four human homologues of the Drosophila region-specific homeotic gene spalt (sal), encoding zinc finger proteins of characteristic structure. Mutations of SALL1 on chromosome 16q12.1 cause Townes-Brocks syndrome (TBS, OMIM 107480). We have shown previously that SALL1 acts as a strong transcriptional repressor in mammalian cells when fused to a heterologous DNA-binding domain. Here, we report that SALL1 contains two repression domains, one located at the extreme N-terminus of the protein and the other in the central region. SALL1 fragments with the central repression domain exhibited a punctate nuclear distribution pattern at pericentromeric heterochromatin foci in murine NIH-3T3 cells, suggesting an association between repression and heterochromatin localization. The implications of these findings for the pathogenesis of Townes-Brocks syndrome are discussed.