The nucleotide sequence of human thrombospondin (TS) mRNA has been determined from human fibroblast and endothelial cDNAs. The sequence of 5802 bp begins 110 bp upstream from the initiator codon and includes the entire 3' untranslated region (UTR) of the mRNA. The coding region (3510 bp) specifies a protein of 1170 amino acids with all of the known features of the TS subunit (Frazier, W. A. 1987. J. Cell Biol. 105:625-632). The long 3' UTR of 2166 nucleotides is extremely A/T-rich, particularly in the latter half. It contains 37 TATT or ATTT(A) sequences that have been suggested as mediators of the stability of mRNAs for cytokines, lymphokines, and oncogenes (Shaw, G., and R. Kamen. 1986. Cell. 46:659-667). Another unusual feature of the 3' UTR of TS mRNA is a stretch of 42 nucleotides of which 40 are thymidines (uridine in the mRNA) including an uninterrupted sequence of 26 thymidines. This region is flanked by two sets of direct repeats suggesting that it may be an insertion element of retrotranscriptional origin. Comparison of the 3' untranslated region of TS mRNA with the GenBank data base indicates the greatest degree of similarity with an alpha-interferon gene which contains a number of the TATT/ATTT consensus sites. The degree of similarity between the TS and interferon sequences is the same in regions of the interferon gene corresponding to its coding and noncoding regions suggesting that most of the TS 3' UTR may be derived from an interferon gene or pseudogene. The features of the TS mRNA 3' UTR provide a potential explanation for the rapid regulation of TS message observed in cultured cells in response to PDGF and suggest that TS is a member of a group of proteins which are intimately involved in the control of cell growth and differentiation.

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