Intranuclear targeting of AML/CBFα regulatory factors to nuclear matrix-associated transcriptional domains

The AML/CBF alpha runt transcription factors are key regulators of hematopoietic and bone tissue-specific gene expression, These factors contain a 31-amino acid nuclear matrix targeting signal that supports association with the nuclear matrix, We determined that the AML/CBF alpha factors must bind to the nuclear matrix to exert control of transcription, Fusing the nuclear matrix targeting signal to the GAL4 DNA binding domain transactivates a genomically integrated GAL4 responsive reporter gene. These data suggest that AML/CBF alpha must associate with the nuclear matrix to effect transcription, We used fluorescence labeling of epitope-tagged AML-1B (CBFA2) to show it colocalizes with a subset of hyperphosphorylated RNA polymerase II molecules concentrated in foci and linked to the nuclear matrix, This association of AML-1B with RNA polymerase II requires active transcription and a functional DNA binding domain, The nuclear matrix domains that contain AML-1B are distinct from SC35 RNA processing domains, Our results suggest two of the requirements for AML-dependent transcription initiation by RNA polymerase II are association of AML-1B with the nuclear matrix together with specific binding of AML to gene promoters.