THE MESSENGER-RNAS FOR CYCLIN-A, C-MYC AND RIBOSOMAL-PROTEINS L4 AND S6 ARE ASSOCIATED WITH CYTOSKELETAL-BOUND POLYSOMES IN HEPG2 CELLS

Cytosolic, cytoskeleton and membrane fractions were extracted from HepG2 cells by a sequential detergent/salt extraction procedure. The cytosolic fraction contained 93% of the lactic dehydrogenase activity while the cytoskeleton fraction was enriched in action and vimentin. The distribution of mRNAs for c-myc, glucose transporter 1, ribosomal proteins L4 and S6 and cyclin A were investigated by Northern hybridization of total RNA extracted from polysomes isolated from cytosolic, cytoskeleton and membrane fractions. The membrane-bound polysomes were enriched in the glucose transporter 1 mRNA and the cytoskeleton-bound polysomes were enriched in the mRNAs for the two ribosomal proteins, c-myc and cyclin A. The results suggest that the mRNAs for nuclear proteins are one class of mRNAs which are translated on polysomes associated with the cytoskeleton; this may be related to the requirement to transport the newly synthesized protein to the nucleus.