A tobacco nuclear protein that preferentially binds to unmethylated CpG-rich DNA.

The methylation of cytosine residues in CpG dinucleotides of eukaryotic DNA is an important mechanism for the regulation of gene expression. Higher plants have a high content of methylated cytosine residues in CpG as well as CpNpG sites, and experimental evidence suggests a role in gene expression for DNA methylation. In this article, we describe a tobacco nuclear protein whose binding to various DNA sequences is positively correlated with the CpG density of the probes. This protein, CpG-binding protein 1 (CGBP-1), has reduced affinity for DNA when the CpG sites are methylated. Ribonuclease treatment also reduces the formation of the CGBP-1 complex. The binding characteristics of CGBP-1 make it an interesting protein with respect to methylation-mediated gene expression in plants.