This family consists of MyoD family inhibitor (I-mfa, MDFI) and MyoD family inhibitor domain-containing protein. I-mfa acts as a transcriptional activator or repressor. It retains nuclear Zic family proteins (ZIC1, ZIC2 and ZIC3) in the cytoplasm and consequently inhibits their transcriptional activation ability []. I-mfa domain-containing protein interacts with HAND1 (bHLH transcription factor), leading to sequester HAND1 into the nucleolus and prevent its activity []. In humans modulates the expression from both cellular and viral promoters. It down-regulates Tat-dependent transcription of the human immunodeficiency virus type 1 (HIV-1) LTR by interacting with HIV-1 Tat and Rev and impairing their nuclear import, probably by rendering the NLS domains inaccessible to importin-beta. It also stimulates activation of human T-cell leukemia virus type I (HTLV-I) LTR [, , ]. Both I-mfa and I-mfa domain-containing protein interact with the axin complex and affect axin regulation of both the Wnt and the JNK activation pathways [].
