REVERSAL OF CREATINE-KINASE TRANSLATIONAL REPRESSION BY 3' UNTRANSLATED SEQUENCES

A subline of U937 cells (U937D) was obtained in which creatine kinase B (CK-B) messenger RNA was present and bound to ribosomes, but CK activity was undetectable. Transformation of U937D cells with retrovirus vectors that contain the 3′ untranslated region (3′ UTR) of CK-B messenger RNA exhibited CK activity with no change in abundance of CK-B mRNA. The 3′ UTR formed a complex in vitro with a component of S100 extracts from wild-type cells. This binding activity was not detectable in S100 extracts from cells that expressed CK activity after transformation with the 3′ UTR-containing vector. These results suggest that translation of CK-B is repressed by binding of a soluble factor or factors to the 3′ UTK.