CYS(2) HIS(2) ZINC-FINGER PROTEIN FAMILY OF PETUNIA - EVOLUTION AND GENERAL MECHANISM OF TARGET-SEQUENCE RECOGNITION/

The EPF family is a group of Cys(2)/His(2) zinc-finger proteins in pet unia, In these proteins, characteristically long spacer regions have b een found to separate the zinc fingers, Our previous DNA-binding studi es demonstrated that two-fingered proteins (ZPT2-1 and ZPT2-2), which have spacers of different lengths, bind to two separate AGI core motif s in a spacing specific manner, To investigate the possibility that th ese proteins might distinguish between the target sequences on the bas is of spacing between the core motifs, we screened petunia cDNA librar y for other proteins belonging to this family, initial screening by PC R and subsequent cloning of full-length cDNAs allowed us to identify t he genes for 10 new proteins that had two, three or four zinc fingers, Among the two-fingered proteins the spacing between zinc fingers vari ed from 19 to 65 amino acids, The variation in the length of spacers w as even more extensive ii-a three-and four-fingered proteins. The pres ence of such proteins is consistent with our hypothesis that the spaci ng between the core motifs might be important for target sequence reco gnition. Furthermore, comparison of diverse protein structures suggest s that three-and two-fingered proteins might have resulted due to succ essive loss of fingers from a four-fingered protein during molecular e volution, We also demonstrate that a highly conserved motif (QALGGH) a mong the members of EPF family acid other Cys(2)/His(2) nine-finger pr oteins in plants is critical for the DNA-binding activity.