In this report, we confirm the existence of the hairpin structure within the 3 0 UTR of the Pol b mRNA and demonstrate that this element influences the expression of a reporter gene. We describe the identification of a protein factor binding to this motif-Hax-1, an anti-apoptotic, cytoskeleton-related protein, which is known to bind a hairpin structure within the 3 0 UTR of vimentin mRNA. We demonstrate that binding occurs only for a Hax-1 dimer, though RNA binding is not a prerequisite for the dimerization itself. We confirm the importance of the hairpin structure for binding of Hax-1 by its mutagenic disruption, which impairs the RNA-protein interaction. We also report strong association of Hax-1 with the nuclear matrix, which is a novel finding, consistent with its transcript-binding properties. Taken together, these data suggest that the hairpin element within the Pol b 3 0 UTR represents a novel motif important for posttranscriptional regulation of expression.