The Transcription Factor LACS from Kh yverom yces Zactis-like GAL4 from Saccharom yces cerevisiae Forms a Zn(II)&yse Binuclear Cluster*

The DNA binding domain of the transcription factor LAC9 contains 6 cysteine residues with spacing in the primary peptide sequence identical to that found in the DNA binding domain of the GAL4 transcription factor. In GAL4, the CysX&ysX&ysX&ysX&ysX&ys motif has been shown to form a Zn(I&Cyss binuclear cluster (Pan, T. and Coleman, J. E. (1990) Proc. N&Z. Acud. Sci. U. S. A. 87, 2077-2081), representing a new structure for a Zn(II)-containing transcription factor which differs from the “zinc finger” motif first described for TFIIIA. LACS has been shown to bind two Zn(I1) ions (Halvorsen, Y. C., Nandabalan, K., and Dickson, R. D. (1990) J. Biol. Chem. 265, 1328313289). The similarity of the amino acid sequence and the Cys spacing within the DNA binding domain suggest that LACS should also be capable of forming the Zn(II)&yse cluster found in GAL4. A fragment of LACS consisting of 144 amino acid residues spanning the DNA binding domain has been prepared with 113Cd(II) substituted for the two native Zn(I1) ions. ‘13Cd NMR of this fragment (denoted LAC9(85-228*)) has been carried out in an attempt to test the hypothesis that LACS, like GAL4, forms a binuclear cluster. The chemical shifts of the two bound l13Cd(II) ions, 705 and 692 ppm respectively, are consistent with ligation of each “‘Cd(II) ion to 4 sulfur atoms. The best model for such ligation is that two of the cysteine Sform bridges between the two Cd(I1) ions. Formation of a Zn(II)-Cd(I1) hybrid form of LAC9(85-228*) has also been observed. We conclude that LACS contains a Zn(II)&yse binuclear cluster as previously reported for GALI.