THE PUR ELEMENT STIMULATES TRANSCRIPTION AND IS A TARGET FOR SINGLE STRAND-SPECIFIC BINDING-FACTORS CONSERVED AMONG VERTEBRATE CLASSES

The PUR element has originally been defined in human, as a purine-rich motif present in a DNA replication initiation zone, whose purine stra nd is capable of binding a single strand-specific factor termed Pur, p resent in HeLa cell nuclear extracts. We have identified a related DNA element, in the 5' region of the quail clusterin gene, for its positi ve influence on the transcription of this gene. In the present work, w e show that this element does correspond to a novel cis-element of tra nscription, still active when placed in an heterologous promoter. We a lso present a series of evidences showing that the avian PUR-specific binding factors are closely related to those previously identified in human. The human Pura protein is capable of binding the quail clusteri n PUR element as well as the human c-myc gene-derived PUR element. UV- crosslinking and Southwestern analyses reveal that the Pur factors pre sent in HeLa and avian cells are closely related. The physical interac tions with the PUR motif of Pura and of the avian Pur factor are ident ical, as shown by PUR mobility-shift assay and methylation interferenc e. Our results suggest that, in addition to their possible involvement in the initiation of DNA replication, these Pur factors are likely to act as transcription trans-activators.