A ROLB REGULATORY FACTOR BELONGS TO A NEW CLASS OF SINGLE ZINC-FINGERPLANT-PROTEINS

A protein which binds to the regulatory domain B necessary for express ion of the plant oncogene rolB in (root) meristems contains a single z inc finger of a novel type conserved in dicots and monocots. Band shif t analysis revealed the presence in tobacco nuclei of a protein select ively binding to domain B, a tetramer of which was used to isolate a c DNA (NtBBF1, Nicotiana tabacum rolB domain B factor 1) from a tobacco expression library, The corresponding genomic clone was also isolated. The protein encoded by NtBBF1 contains a single C2C2 zinc finger, and its target sequence in domain B was identified by means of mutagenize d oligonucleotides. The DNA-binding capability of the zinc finger was assessed by means of a fusion of this latter with the glutathione-S-tr ansferase protein, that was shown to bind the same target sequence as NtBBF1. A number of other tobacco cDNAs encoding different proteins wi th a domain (BBF domain) encompassing the zinc finger identical to NtB BF1 were also isolated. Furthermore, a cDNA encoding a protein with an almost identical single zinc finger was isolated from Arabidopsis. A very closely related zinc finger has very recently been identified in maize transcription factors and termed the Dof domain. It is proposed that the tobacco, Arabidopsis and maize BBF/Dof domain proteins are me mbers of a new broad family of plant transcription factors acting thro ugh a single zinc finger widely utilized in the plant kingdom.