gene during the mammalian UV response. Rapid and preferential activation of the c-jun

induced by these agents, it was con-ceivable that the AP-1 activity induced by TPA containsmorec-Jun-c-Fos heterodimers than the activity induced byUVor H202. However, the use of Fos antibodies (Fig. 6)indicates that after several hours, the AP-1 complexes in-duced by TPA, UV, and H202 contain similar amounts ofc-Fos protein. Therefore, it is unlikely that the AP-1 com-plexes induced by the different agents control differentsubsets of genes. In fact, at least two AP-1 target genes,collagenase and metallothionein