Ten ERK-related proteins in three distinct classes associate with AP-1 proteins and/or AP-1 DNA

We have identified seven ERK-related proteins ("ERPs"), including ERK2, tha t are stably associated in vivo with AP-1 dimers composed of diverse Jun an d Fos family proteins. These complexes have kinase activity. We designate t hem as "class I ERPs." We originally hypothesized that these ERPs associate with DNA along with AP-1 proteins. We devised a DNA affinity chromatograph y-based analytical assay for DNA binding, the "nucleotide affinity preincub ation specificity test recognition" (NAPSTER) assay. In this assay, class I ERPs do not associate with AP-1 DNA. However, several new "class II" ERPs do associate with DNA. p41 and p44 are ERK1/2-related ERPs that lack kinase activity and associate along with AP-1 proteins with AP-1 DNA. Class I ER- Ps and their associated kinase activity thus appear to bind AP-1 dimers whe n they are not bound to DNA and then disengage and are replaced by class II ERPs to form higher order complexes when AP-1 dimers bind DNA p97 is a cla ss HI ERP, related to ERK3, that associates with AP-1 DNA without AP-1 prot eins. With the exception of ERK2, none of the 10 ERPs appear to be known mi togen-activated protein kinase superfamily members.