Kinetic studies of Fos center dot Jun center dot DNA complex formation: DNA binding prior to dimerization

The bZIP proteins Fos and Jun bind DNA rapidly and with high affinity, form ing a heteromeric complex that mediates activated transcription. Here we us e stopped-flow fluorescence resonance energy transfer (FRET) to study the k inetic pathway by which Fos Jun DNA complexes assemble, Though dimerization of Fos and Jun occurs rapidly in the absence of DNA, the rate of dimerizat ion is enhanced in the presence of DNA, Global analysis of the kinetic data shows that the favored DNA binding pathway is one is which the two protein monomers bind DNA sequentially and assemble their dimerization interface w hile bound to DNA.