Several DNA binding NF-kappaB subunits are substrates for cGMP-dependant kinase (PKG) and their transactivation from cognate sites is induced by phosphorylation. This includes p50, which does not have a transcriptional activation domain and therefore needs to bind to other proteins to mediate gene expression. Here, we describe the synergistic transactivation by p50 and PKG from the CMV promoter. This is caused not only by phosphorylation of p50, leading to increased DNA binding, but also by PKG-dependant activation of CRE sites in the promotor. One of the CRE sites is located directly adjacent to a NB-kappaB site and is essential for p50-mediated induction of transcription. According to the binding of CREB to p50 in pull-down assays and according to the inhibition of p50-dependant transactivation by dominant-negative CREB, this reflects the formation of a transcription factor complex containing CREB and p50. This nuclear translocation of NF-kappaB is insufficient to distinguish among the multitude of promotors that harbor cognate recognition sites. The phosphorylation of multiple transcription factors by an upstream kinase, such as PKG, can lead to the formation of transcription factor complexes and differential transactivation from a subset of NF-kappaB sites. These interactions may be relevant for the activation of viral gene expression. (C) 2004 Elsevier Inc. All rights reserved.