Basonuclin: a keratinocyte protein with multiple paired zinc fingers.

A cDNA clone has been prepared from mRNA of cultured human keratinocytes. The sequence of the cDNA reveals that in the C-terminal two-thirds of the corresponding protein (basonuclin), there are three separated pairs of adjacent zinc fingers. The amino acid sequence of each pair is homologous to that of the single pair of zinc fingers of the Drosophila transcription factor encoded by disco. Near the C-terminal end of basonuclin and on the surface of a putative alpha-helix, there is a stripe of serine residues similar to that of the transcription factor PRDII-BF1. Basonuclin possesses a sequence of six amino acids quite similar to one present in the myogenic family of proteins, including Myf5; this sequence is located in the omega loop of the myogenic proteins but within a zinc finger of the keratinocyte protein. As basonuclin is present mainly in the nuclei of the basal cell layer, its regulatory function is likely to be exerted prior to the process of terminal differentiation.