A human liver cDNA library enriched for full-length clones was screened for plasminogen cDNA using a synthetic 24nucleotide probe derived from a reported partial cDNA sequence. 12 positive clones were identified and one of these was characterized in detail. The 2.7 kb insert contains the complete coding region. At 5 positions, it gives residues different from those reported in a previous amino acid sequence analysis of the protein. The present results show an extra IIe at position 65. Gln instead of Glu at positions 53 and 342, Asn at position 88 instead of Asp, and Asp at position 453 rather than Asn. In the 3'-non-coding region an extension of 29 bases is found which does not contain any structure compatible with a known polyadenylation signal. Instead, the consensus signal AATAAA is placed at a distance of 46 bases upstream of the poly(A)-tail.
Two different insulin‐like growth‐factor (IGF)‐binding proteins have been found in human blood, one of high molecular mass and dependent on growth hormone for synthesis, the other of low molecular mass and independent of growth hormone. The small IGF‐binding protein is abundant in human amniotic fluid. Its amino acid sequence has now been determined by direct analysis of the protein and its proteolytic fragments. Also, by immunoscreening a partial cDNA clone was isolated from a human hepatoma cell line. The mature protein consists of 234 amino acids and is coded for by an mRNA of approximately 1700 nucleotides in length. The primary structure of the protein reveals 18 Cys residues in N‐terminal and C‐terminal clusters and an Arg‐Gly‐Asp peptide sequence, common to extracellular proteins binding to receptors of the integrin family. A protein‐sequence polymorphism was detected at position Ile/Met‐228, indicating possible allelic variation. The 3′‐untranslated mRNA sequence has a high A + T content and shows five copies of an ATTTA sequence which has been shown to be involved in the regulation of the stability of certain mRNAs coding for growth‐regulating proteins.
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