Unmethylated CpG islands are known to keep adjacent promoters transcriptionally active. In the CpG island adjacent to the adenosine phosphoribosyltransferase gene, the protection against transcriptional silencing can be attributed to the short CpG-rich core element containing Sp1 binding sites. We report here the insertion of this CpG island core element, IE, into the long terminal repeat of a retroviral vector derived from Rous sarcoma virus, which normally suffers from progressive transcriptional silencing in mammalian cells. IE insertion into a specific position between enhancer and promoter sequences led to efficient protection of the integrated vector from silencing and gradual CpG methylation in rodent and human cells. Individual cell clones with IE-modified reporter vectors display high levels of reporter expression for a sustained period and without substantial variegation in the cell culture. The presence of Sp1 binding sites is important for the protective effect of IE, but at least some part of the entire antisilencing capacity is maintained in IE with mutated Sp1 sites. We suggest that this strategy of antisilencing protection by the CpG island core element may prove generally useful in retroviral vectors.

• MeSH
• Models, Biological MeSH
• CpG Islands * MeSH
• Transcription, Genetic * MeSH
• Terminal Repeat Sequences MeSH
• Humans MeSH
• Mutation MeSH
• Flow Cytometry MeSH
• Sarcoma, Avian genetics   virology   MeSH
• Birds MeSH
• Genes, Reporter MeSH
• Sp1 Transcription Factor metabolism   MeSH
• Gene Silencing * MeSH
• Binding Sites MeSH
• Avian Leukosis Virus metabolism   MeSH
• Rous sarcoma virus metabolism   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Sp1 Transcription Factor MeSH