Changes in the type II and type I collagen messenger RNA population during growth of chondrocytes in 5-bromo-2-deoxyuridine.

The collagen mRNA population of cultured chick chondrocytes was examined during a 5-bromo-2-deoxyuridine-induced shift in the type of collagen synthesized. When a cell-free protein-synthesizing system was used, it was found that an increase in the translatable mRNA for type I collagen [alpha 1 (I)]2 alpha 2 was correlated with the onset of the synthesis of this collagen type by intact cells. It was also found, both in vivo and in vitro, that a normal 2:1 ratio of type I subunits is not synthesized at early times in the type II to type I shift but that the alpha 1 (I) subunit is found in excess. It would appear, therefore, that the expression of these complementary subunits is not tightly coordinated.