How transcription factors regulate gene transcription on chromatin is the central question of the study of gene expression regulation. Recent investigations showed that regulatory factors form different complex in nucleus such as RNA polymerase Ⅱ holoenzyme, chromatin remodeling complexes, nucleosome and enhanceosome, which participate each step of gene transcription and assemble into active transcription complex. Formation of these complexes integrates lots of information of transcription regulation and increase the efficiency of transcription, which is the basis of orderly efficient expression of genes. On the other hand, it is a challenge to study these transcription complexes and development of new technology is important.