E1

E1 is an alphanumeric designation that appears in several unrelated domains. There is no single definition; the term is used in telecommunications, road transport, government immigration policy, and science to denote different concepts.

In telecommunications, E1 is the European digital transmission format used in PDH networks. It operates at 2.048 megabits per second and provides 32 timeslots of 64 kilobits per second. Of these, 30 channels are typically used for 64 kbps speech circuits, with timeslot 0 carrying framing information and signaling.

European route E1 is part of the United Nations E-road network. It designates a north–south corridor extending from Larne in Northern Ireland to Seville in Spain, connecting Ireland, the United Kingdom, France, and the Iberian Peninsula.

E-1 visa: The E-1 treaty trader visa is a United States nonimmigrant visa for nationals of countries that maintain a treaty of commerce and friendship with the U.S. It allows entrants to engage in substantial international trade, principally in goods or services, on behalf of a qualifying treaty trader. Initial stays typically up to two years, with extensions; dependents may accompany.

E1 enzyme: In biochemistry, E1 denotes the ubiquitin-activating enzyme, the first enzyme in the ubiquitination cascade. E1 activates ubiquitin in an ATP-dependent manner and transfers it to an E2 conjugating enzyme, enabling tagging of proteins for degradation by the proteasome.

E1 transitions: In spectroscopy, E1 denotes electric-dipole allowed transitions, the most common type of radiation-induced transitions in atoms and molecules, subject to selection rules related to angular momentum.