The B-box zinc finger is an around 40 amino acids domain. One or two copies of this motif are generally associated with a RING finger and a coiled coil motif to form the so-called tripartite motif. It is found essentially in transcription factors, ribonucleoproteins and proto-oncoproteins, but no function is clearly assigned to this domain [1]. It has been shown to be essential but not sufficient to localize the PML protein in a punctate pattern in interphase nuclei [2].

Among the 7 possible ligands for the zinc atom contained in a B-box, only 4 are used and bind one zinc atom in a Cys2-His2 tetrahedral arrangement. The NMR analysis reveals that the B-box structure comprises two β-strands, two helical turns and three extended loop regions different from any other zinc binding motif [3].

Proteins currently known to include the zinc finger B-box domain are listed below:

• Mammalian ARD1 protein. GTP-binding protein.
• Mammalian PML, probable transcription factor. Involved in a form of acute promyelocytic leukemia (APL).
• Mammalian TIF1, transcription intermediary factor 1. Interacts selectively in vitro with the AF2-activating domain of the estrogen receptors.
• Mammalian RFP, ret finger Protein. May function in male germ cell development.
• Human 52 Kd RO/SS-A protein. A protein of unknown function from the RO/SS-A ribonucleoprotein complex.
• Human HT2A may play a significant role in mediating the biological activity of the HIV-1 tat protein in vivo. Binds specifically to the activation domain of HIV-1 tat and can also interact with the HIV-2 and EIAV tat proteins in vivo.
• Mouse RPT1, trans-acting factor that regulates gene expression of interleukin 2 receptor α chain and of human immunodeficiency virus type 1.
• PwA33, associated with the lambrush chromosome loops in Pleurodeles Waltlii, may function as a component of Ribonucleoprotein complexes.
• Xenopus laevis XNF7 (Xenopus nuclear factor 7) protein. There are two isoformes (XNF7-O and XNF7-B) of this DNA binding protein. The B-box domain of XNF7-B was analysed by NMR [3].

We developed a profile that covers the whole domain.