PURIFICATION AND CHARACTERIZATION OF A MULTICOMPONENT AP-1 JUND COMPLEX FROM T-CELLS - DEPENDENCE ON A SEPARATE CELLULAR FACTOR FOR ENHANCED DNA-BINDING ACTIVITY

TAP-1 (T-cell AP-1) is a previously identified DNA-binding activity th at is rapidly induced in activated T cells in the absence of protein s ynthesis, This activity has been purified over 2,000-fold from the T-c ell line MLA144. Purified TAP-1 is a multicomponent complex composed o f 38-kDa and 43-kDa junD polypeptides in association with a separate f actor(s), distinct from fos, that partly dissociate from the complex d uring affinity purification but is required for full TAP-1 DNA-binding activity. When reconstituted with TAP-1, this partly dissociated comp onent strongly enhances the DNA-binding activity of the TAP-1 complex. W-cross linking analysis identifies the dissociable component of the TAP-1 complex as a separate class of low molecular mass (23-29-kDa) DN A-binding polypeptide(s). 23-29-kDa polypeptides have been partially p urified from nuclear extracts derived from MLA144 that enhance TAP-1 D NA-binding activity over 100-fold and increase its contacts with flank ing DNA sequence. These results define TAP-1 as a distinct AP-l junD-c ontaining complex in T cells whose DNA-binding activity is regulated b y the interaction of distinct and separate cellular factor(s).