The c-myb proto-oncogene product binds to but does not activate the promoter of the DNA polymerase alpha gene.

The myb proto oncogene product (c-Myb) is a transcriptional regulator and its expression and function are tightly linked to the cellular entry into S phase and DNA synthesis. It has been shown [Venturelli, D., Travali, S. & Calabretta, B. (1990). Proc. Natl. Acad. Sci. USA, 87, 5963-5967] that inhibition of T-cell proliferation by a myb antisense oligomer is accompanied by down-regulation of DNA polymerase alpha expression. To examine whether the transcription of the DNA polymerase alpha gene is directly regulated by c-Myb, we have identified and characterized the 5' regulatory region of the human DNA polymerase alpha gene. Two major and several minor transcription start sites were identified by nuclease S1 mapping. DNA sequence analysis showed that the promoter region contains no TATA box, one CCAAT box and putative Ap-1, AP-2 and E2F binding sites. In DNAase I footprinting, the bacterially expressed c-Myb protected six sites in the 5' flanking region of the human DNA polymerase alpha gene. However, c-Myb did not activate the DNA polymerase alpha gene promoter in a co-transfection assay. Our results suggest that an unknown factor(s) is required for the c-Myb-induced activation of the DNA polymerase alpha gene promoter, or c-Myb does not directly activate this promoter.