CHARACTERIZATION OF THE HUMAN RB1 PROMOTER AND OF ELEMENTS INVOLVED IN TRANSCRIPTIONAL REGULATION

The retinoblastoma gene (RB1) is a recessive oncogene implicated in a number of human tumors. Although the RB1 gene is expressed in most pro liferating cells, there is considerable evidence for the transcription al regulation of this gene. Therefore, we have performed a detailed an alysis of the regulatory elements in the promoter of the human RB1 gen e. Deletion analysis of the 5' upstream region determined the location of the basal promoter to be between -208 and -179 nucleotides relativ e to the translational start. This region contains essential binding s ites for the transcription elements ATF and SP1 and potentially import ant sites for E2F and steroid hormone responsiveness but no TATA or CA AT boxes. Primer extension and RNase protection analysis identified tw o initiation sites at -176 and -128 base pairs, both downstream of the promoter. Cotransfection experiments revealed repression of the RBI p romoter by its protein product p110(RB1). This repression has been map ped to the core promoter region containing the E2F-binding site; howev er, this site is not required for autorepression.