REGULATION OF THE HUMAN POLY(ADP-RIBOSYL) TRANSFERASE PROMOTER VIA ALTERNATIVE DNA RACKET STRUCTURES

Human nuclear poly(ADP-ribosyl) transferase (ADPRT) protein content in cells suggests that ADPRT expression is stringently controlled. Analy sis of the 3 kb promoter sequence, which is required for high level ex pression, revealed an extraordinary architecture: several Spl motifs a re located in the vicinity of the first exon but the closest CCAAT/TAT A boxes are several hundred basepairs away. Four Alu type repetitive s equences are in the promoter structure. Within these Alu sequences the ra exist inverted repeat elements, which could form two mutually exclu sive types of DNA tertiary structure consisting of quadruplex DNA and loops resembling rackets. Thereby, a CCAAT/ATA element would be moved to spatial vicinity of the Spl site activating the promoter. Deletion analysis showed the functional significance of these racket elements. We also obtained evidence for DNA racket structures when we studied mu tational mechanisms in a human adenine phosphoribosyltransferase (APRT ) deficient patient. One of his alleles harbours a novel complex type of deletion/insertion mutation. Based on several highly informative se quence features in this genomic region a model is proposed for the gen eration of this unusual type of mutation involving two steps: an initi al targeting step and a subsequent complex rearrangement. This process includes the formation of a DNA racket structure, which resembles tha t of the ADPRT promoter Thus we conclude that DNA racket structures se em to be of general importance in nature.