Identification and characterization of a JC virus pentanucleotide repeat element binding protein: cellular nucleic acid binding protein.

The JC virus (JCV) control region contains AGGGAAGGGA, the tandem pentanucleotide repeat element (Pnt2). Several proteins specifically interacted via Pnt2 to regulate the expression of JCV early promoter-enhancer (JCV(E)) or late promoter-enhancer (JCV(L)). In this study, a JCV Pnt2 oligonucleotide probe was used to screen a cDNA expression library from glial P19 mouse embryonal carcinoma cells. A cDNA clone was isolated by Southwestern blot assay and it produced a protein that reproducibly and specifically bound to Pnt2. This cDNA had 100% homology to one of three previously identified mouse cDNAs called cellular nucleic acid binding proteins (Cnbps). Cnbps are a highly homologous family of eukaryotic genes implicated in functional interactions with cytoplasmic RNA and regulatory DNA elements. An mRNA of 2.2 kb of Pnt2-interacting Cnbp (PCnbp) was seen in undifferentiated, muscle or glial P19 cells. When expressed from a cDNA expression vector as a fusion protein that also contained 115 kDa from beta-galactosidase, a Pnt2 binding protein (PCNBP) specifically bound to Pnt2 in Southwestern blots as a 30 kDa component of the 145 kDa fusion protein. Furthermore, JCV(E) expression was negatively regulated by PCnbp produced in vivo from the cDNA expression vector. Regulation of JCV(L) was unaffected. We suggest a novel role for CNBP as a PCNBP that interacts with Pnt2 in the negative transcriptional regulation of JCV(E).