Blood coagulation factor X mRNA encodes a single polypeptide chain containing a prepro leader sequence

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Abstract
Thirty thousand colonies of a bovine liver cDNA library were screened with a mixture of synthetic oligodeoxyribonucleotides coding for bovine factor X. Five positive colonies were identified, and plasmid DNA was isolated. Cleavage with restriction endonucleasea showed that these plasmids (designated pBX1-5) contained inserts of 1530bp, 770bp, 700bp, 1100bp and 930bp. DNA sequence analysis of the plasmid with the largest insert (pBX1) confirmed that bovine factor X cDNAs had been cloned. The cDNA sequence predicts that factor X is synthesized as a single chain precursor in which the light and heavy chains of plasma factor X are linked by the dipeptide Arg-Arg. The cDNA sequence also predicts that factor X is synthesized with a prepro leader peptide. We propose that at least five specific proteolytic events occur during the conversion of prepro-factor X to plasma factor Xa.