The capacity of polyomavirus enhancer binding protein 2αB (AML1/Cbfa2) to stimulate polyomavirus DNA replication is related to its affinity for the nuclear matrix

The nuclear matrix is thought to play an important role in the DNA replication of eukaryotic cells, although direct evidence for such a role is still lacking. A nuclear matrix-associated transcription factor, polyomavirus (Py) enhancer binding protein 2 alpha B1 (PEBP2 alpha B1) (AML1/Cbfa2), was found to stimulate Py replication through its cognate binding site. The minimal replication activation domain (RAD) was identified between amino acid (aa) 302 and aa 371 by using a fusion protein containing the GAL4 DNA binding domain (GAL4-RAD). In addition, the region showed affinity for the nuclear matrix and, on the basis of competition studies, binding activity for one or more proteins involved in the initiation of Py DNA replication. A leukemogenic chimeric protein, AML1/ETO(MTG8), which does not contain this region of PEBP2 alpha B1/AML1, was also localized in the nuclear matrix fraction and competed for nuclear matrix association with PEBP2 alpha B1 and GAL4-RAD. Moreover, AML1/ETO inhibited Py DNA replication stimulated by PEBP2 alpha B1 and GAL4-RAD. The inhibition was specific for replication mediated by PEBP2 alpha B1 and GAL4-RAD, and proportional to the degree of loss of these activators from the nuclear matrix, suggesting a requirement for nuclear matrix targeting in the stimulation of Py DNA replication by RAD. These results are the first to suggest a molecular link between the initiation of DNA replication and the nuclear matrix compartment.