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

Abstract

The JC virus (JCV) control region contains AGGGAAGGGA, the tandem pentanucleotide repeat element (Pnt 2). Several proteins specifically interacted via Pnt 2 to regulate the expression of JCV early promoter-enhancer (JCV E) or late promoter-enhancer (JCV L). In this study, a JCV Pnt 2 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 Pnt 2. 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 Pnt 2-interacting Cnbp (P Cnbp) 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 β-galactosidase, a Pnt 2 binding protein (PCNBP) specifically bound to Pnt 2 in Southwestern blots as a 30 kDa component of the 145 kDa fusion protein. Furthermore, JCV E expression was negatively regulated by P Cnbp 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 Pnt 2 in the negative transcriptional regulation of JCV E.