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 strand is capable of binding a single strand-specific factor termed Pur, present in HeLa cell nuclear extracts. We have identified a related DNA element, in the 5' region of the quail clusterin gene, for its positive influence on the transcription of this gene. In the present work, we show that this element does correspond to a novel cis-element of transcription, still active when placed in an heterologous promoter. We also present a series of evidences showing that the avian PUR-specific binding factors are closely related to those previously identified in human. The human Pur alpha protein is capable of binding the quail clusterin PUR element as well as the human c-myc gene-derived PUR element. UV-crosslinking and Southwestern analyses reveal that the Pur factors present in HeLa and avian cells are closely related. The physical interactions with the PUR motif of Pur alpha and of the avian Pur factor are identical, as shown by PUR mobility-shift assay and methylation interference. 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.