Cartilage-specific 5' end of chick alpha 2(I) collagen mRNAs

Chondrocytes grown in suspension contain both type I and type II collagen mRNAs, yet synthesize only type II collagen. The inability of chondrocytes to synthesize the alpha 2 subunit of type I collagen, alpha 2(I), results from a severely reduced translation elongation rate (Bennett, V.D., and Adams, S.L. (1987) J. Biol. Chem. 262, 14806-14814). Furthermore, the alpha 2(I) collagen mRNAs from chondrocytes are translated inefficiently in vitro and appear slightly smaller than those from other cells (Focht, R.J., and Adams, S.L. (1984) Mol. Cell. Biol. 4, 1843-1852). These observations suggest that the reduced translation elongation rate may be due to an intrinsic property of the mRNAs. In this report we demonstrate that the alpha 2(I) collagen mRNAs from suspended chondrocytes are 120 bases shorter than those from other cells, and that the first 94 bases of the chondrocyte mRNAs differ from the corresponding region of the calvaria mRNAs. The unique 5' end of the chondrocyte alpha 2(I) collagen mRNAs accounts for their smaller size and may be responsible for the translation elongation defect. Interestingly, the alpha 2(I) collagen mRNAs from chondrocytes grown in monolayer, rather than in suspension, no longer display the cartilage-specific 5' end, suggesting that cell shape and/or adhesion may modulate the structure of the 5' end of the chondrocyte alpha 2(I) collagen mRNAs.