U1

U1 is a designation used in various fields to denote a line, a component, or other identifiers. Because it appears in different systems, the meaning depends on the context.

In public transit, Berlin U-Bahn line U1 runs roughly east to west across central Berlin, connecting Warschauer Straße with Uhlandstraße. It is one of the system’s oldest lines and is typically shown in brown on maps. In Vienna, U1 is a line of the Vienna U-Bahn that extends from Leopoldau in the north to Reumannplatz in the south. The line is a major north–south route in the city and is colored orange on maps.

In biology, U1 refers to the U1 small nuclear RNA (U1 snRNA), a component of the U1 small nuclear ribonucleoprotein particle involved in recognizing the 5' splice site during pre-mRNA splicing. This RNA plays a critical role in the early steps of spliceosome assembly.

Beyond transit and molecular biology, U1 can appear as a model number, product code, or designation in various technical fields. The exact meaning of U1 is determined by the domain, organization, or system in which it is used.