All viruses target host cell factors for successful life cycle completion. 
Transcriptional control of DNA viruses by host cell factors is important in the 
temporal and spatial regulation of virus gene expression. Many of these factors 
are recruited to enhance virus gene expression and thereby increase virus 
production, but host cell factors can also restrict virus gene expression and 
productivity of infection. CCCTC binding factor (CTCF) is a host cell DNA 
binding protein important for the regulation of genomic chromatin boundaries, 
transcriptional control and enhancer element usage. CTCF also functions in RNA 
polymerase II regulation and in doing so can influence co-transcriptional 
splicing events. Several DNA viruses, including Kaposi's sarcoma-associated 
herpesvirus (KSHV), Epstein-Barr virus (EBV) and human papillomavirus (HPV) 
utilize CTCF to control virus gene expression and many studies have highlighted 
a role for CTCF in the persistence of these diverse oncogenic viruses. CTCF can 
both enhance and repress virus gene expression and in some cases CTCF increases 
the complexity of alternatively spliced transcripts. This review article will 
discuss the function of CTCF in the life cycle of DNA viruses in the context of 
known host cell CTCF functions.