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We have used a subtractive hybridization procedure to isolate cDNA clones for proteins that are produced by human fibroblasts, but not by their SV40-transformed counterparts. With this technique we found, in addition to fibronectin and collagen VI, a novel GTP-binding protein. Sequencing of overlapping cDNA clones demonstrated that this protein is composed of 364 amino acids with a molecular mass of 41 kDa and a calculated isoelectric point of 9.4. It contains the five sequence motifs G1-G5 that are conserved in all GTP-binding proteins. Apart from these characteristic motifs the amino acid sequence differs substantially from those of the well characterized G-proteins, but it is similar to those of some recently identified proteins from Caenorhabditis elegans, from Schizosaccharomyces pombe, and from an archaebacterium, suggesting the existence of a new subfamily within the superfamily of the GTP-binding proteins. The striking conservation of the primary structure between distantly related species indicates a fundamental function of the new protein. Since it is produced in normal, but not in virally transformed fibroblasts, it may play a role in the expression of the transformed phenotype or in growth control.

Original publication




Journal article


The Journal of biological chemistry

Publication Date





25447 - 25453


Laboratorium für Biochemie I, Eidenössische Technische Hochschule Zürich, Switzerland.


Fibroblasts, Humans, Simian virus 40, Cell Transformation, Neoplastic, Cell Transformation, Viral, GTP-Binding Proteins, DNA, Complementary, Restriction Mapping, Cloning, Molecular, Sequence Analysis, DNA, Gene Expression Regulation, Amino Acid Sequence, Base Sequence, Sequence Homology, Amino Acid, Tissue Distribution, Molecular Sequence Data