Members of this family are transcriptional repressors. They may act by increasing histone deacetylase activity at promoter regions [1].

1: hnulp1, a basic helix-loop-helix protein with a novel transcriptional repressive domain, inhibits transcriptional activity of serum response factor. Cai Z, Wang Y, Yu W, Xiao J, Li Y, Liu L, Zhu C, Tan K, Deng Y, Yuan W, Liu M, Wu X; Biochem Biophys Res Commun. 2006;343:973-981. PMID:16574069