A printing unit of a printing press includes at least two frame parts whose distance from each other can be varied. Each of these frame parts include two laterally spaced frame plates. The two frame plates in each of the frame parts accommodate at least one cylinder or roller which extends between them. The two lateral frame plates in each frame part are spaced from each other in an axial direction of the supported cylinder or roller. Adjacent ones of the frame parts are connectable to each other by abutting of their respective lateral frame plates. At least three locking and/or centering devices are used to align and to lock together the lateral frame plates of adjacent ones of the frame parts.