The terminal differentiation of postmitotic oligodendrocytes is marked by the induction of myelin-specific genes. In this report, we demonstrate that culture conditions that induce oligodendrocyte differentiation of glial progenitor cells also induce differentiation of C6 glioblastoma cells, as monitored by activated transcription of the gene encoding proteolipid protein (PLP), the major myelin protein of the CNS. When assayed by transfections of hybrid reporter plasmids, the transcriptional control region of the PLP gene is preferentially active in differentiated C6 cells and contains both positive and negative cis-regulatory elements. In general, functional identification of these elements is well correlated with the binding sites of glial nuclear proteins, as visualized by the presence of DNase I-protected footprints. A sequence within one positive cis-regulatory element of the PLP gene is conserved in the control regions of three other myelin- specific genes, suggesting that their coordinate transcription may involve a common regulatory mechanism.