A20

A20 is a designation used in several unrelated fields to label roads, biological genes, and aircraft. Because of this variety, the term does not refer to a single topic but to multiple entries across different contexts.

In transportation, A20 indicates major roads or highways in several countries. In the United Kingdom, the A20 is a primary road; similarly named routes exist in other countries, where such A roads typically serve as important regional links. The exact routes and endpoints vary by country and over time, with some A20 roads serving as connections to ports or capitals.

In biology, A20 refers to the TNFAIP3 gene, which encodes the A20 protein. A20 is a ubiquitin-editing enzyme that functions as a negative regulator of the NF-kB signaling pathway, helping to control inflammation. Loss-of-function mutations or haploinsufficiency of TNFAIP3 have been associated with autoimmune and autoinflammatory diseases, including various forms of arthritis and inflammatory bowel disease, among others. The protein participates in ubiquitination and deubiquitination processes that modulate immune responses.

In aviation, the A-20 Havoc was a twin-engine light bomber and ground-attack aircraft used by the United States Army Air Forces and Allied air forces during World War II. It entered service in the early 1940s and remained in various roles through the mid-1940s, with multiple operators and several variants produced by Douglas Aircraft.