Abstract: Lock-up assemblies clamp a flexible print plate to a circumferential surface of the print plate cylinder. Preferably, the print plate lock-up assemblies are adapted to being received within a gutter of a print plate cylinder and include an elongate support bar assembly, and a jaw assembly supported by the support bar assembly and adapted for positionally clamping a print plate to an exterior circumferential surface of the print plate cylinder. Preferably, the jaw assemblies include a pair of retainer blocks which are spaced from one another along the support bar assembly, and a jaw support plate positioned between the pair of retainer blocks and adapted for movement along the pair of retainer blocks towards and away from the support bar. A pair of mirror-imaged jaw members is positioned upon and supported by said jaw support plate.