U4

U-4, U04 or U4 may refer to:

U4 spliceosomal RNA, a non-coding RNA component of the major U2-dependent spliceosome
Anti-Corruption Resource Centre, based at the Chr. Michelsen Institute in Bergen, Norway
Haplogroup U4 (mtDNA), a human genetic group
U4, an unemployment figure released by the United States Bureau of Labor Statistics
U04, Severe acute respiratory syndrome ICD-10 code
U4, unitary group of degree 4
Ultima IV: Quest of the Avatar, a video game
U-47700, a synthetic opioid

Transport

Underground railways
- U4 (Berlin U-Bahn), a subway line in Berlin, Germany
- U4 (Frankfurt U-Bahn), a subway line in Frankfurt, Germany
- U4, a Hamburg U-Bahn line
- U4, a Munich U-Bahn line
- U4, a Vienna U-Bahn line.
German submarine U-4, one of several German submarines
London Buses route U4
U-4, the U.S. Air Force version of the Aero Commander (aircraft), a light twin-engined aircraft from Aero Design and Engineering Company
U-4, the Japanese air self-defense force designation for the Gulfstream IV aircraft
U4, PMTair (former) IATA airline designator
U4, Buddha Air current IATA airline designator