We have previously identified in endothelial cells a gene product designated A20, that is rapidly and profoundly induced by tumor necrosis factor alpha (Dixit, V. M., Green, S., Sarma, V., Holzman, L. B., Wolf, F. W., O'Rourke, K., Ward, P. A., Prochownik, E. V., and Marks, R. M. (1990) J. Biol. Chem. 265, 2973-2978). Isolation of the full-length cDNA followed by sequence analysis has revealed that A20 codes for a novel zinc finger protein. Structural features suggest that this putative protein, which contains multiple Cys2/Cys2 finger motifs, defines a novel class of zinc finger proteins. Southern analysis supports the existence of other members of the class.