InterPro domain: IPR035925

The BSD domain is an about 60-residue long domain named after the BTF2-like transcription factors, Synapse-associated proteins and DOS2-like proteins in which it is found. Additionally, it is also found in several hypothetical proteins. The BSD domain occurs in one or two copies in a variety of species ranging from primal protozoan to human. It can be found associated with other domains such as the BTB domain (see PDOC50097 ) or the U-box in multidomain proteins. The function of the BSD domain is unknown [ 1 ].

Secondary structure prediction indicates the presence of three predicted alpha helices, which probably form a three-helical bundle in small domains. The third predicted helix contains neighbouring phenylalanine and tryptophan residues - less common amino acids that are invariant in all the BSD domains identified and that are the most striking sequence features of the domain [ 2 ].

Some proteins known to contain one or two BSD domains are listed below:

• Mammalian TFIIH basal transcription factor complex p62 subunit (GTF2H1).
• Yeast RNA polymerase II transcription factor B 73kDa subunit (TFB1), the homologue of BTF2.
• Yeast DOS2 protein. It is involved in single-copy DNA replication and ubiquitination.
• Drosophila synapse-associated protein SAP47.
• Mammalian SYAP1.
• Arabidopsis thaliana (Mouse-ear cress) TFB1-1 (TFB1A) and TFB1-3 (TFB1C).

1. BSD: a novel domain in transcription factors and synapse-associated proteins. Trends Biochem. Sci. 27, 168-70