About 8% of human genes have been estimated to carry out transcription from both DNA strands, resulting in significant level of endogenous antisense RNA. In cytoplasm the antisense RNA leads to formation of long dsRNA, which activates the interferon and RNA-dependent protein kinase antiviral pathway. Most endogenous antisense RNA is made in nucleus and two responses have been suggested for the nuclear dsRNA. First, the dsRNA may be processed by enzymes of the family of adensoine deaminases that act on RNA (ADAR). The deaminated dsRNAs contain various levels of inosines. dsRNA containing high level of inosines are tightly bound by a protein complex that results in their nuclear retention. dsRNA containing low level of inosines may be able to exit the nucleus. Second, the nuclear dsRNA can lead to gene silencing and heterochromatin formation.