Enhancers increase the probability but not the level of gene expression.
Transcriptional enhancers act in cis to suppress position-effect variegation.
Overcoming globin gene silencing in gene therapy vectors. The globin genes have long been the focus of intense study, because they are altered by many mutations that cause hereditary anemias with wide-ranging and often devastating effects. The well-characterized molecular basis for hemoglobinopathies like sickle cell disease has made these disorders natural targets for replacement gene therapy. A major obstacle to gene therapy for these and other disorders is the silencing of transcription that occurs after genomic integration of replacement gene vectors. This silencing may reflect widely described mechanisms that silence ectopically integrated genes.