Inspired by a statement of W. Luh asserting the existence of entire functions having together with all their derivatives and antiderivatives some kind of additive universality or multiplicative universality on certain compact subsets of the complex plane or of, respectively, the punctured complex plane, we introduce in this paper the new concept of U-operators, which are defined on the space of entire functions. Concrete examples, including differential and antidifferential operators, composition, multiplication and shift operators, are studied. A result due to Luh, Martirosian and Miiller about the existence of universal entire functions with gap power series is also strengthened.2000 Mathematics subject classification: primary 30E10; secondary 47A16, 47B33, 47B38, 47E05, 47G10.