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A 4-kilobase and a 2-kilobase cDNA clone encoding a murine macrophage colony-stimulating factor have been isolated. Except for 2 amino acid residue differences, these two clones encode the same 520 amino acid residue protein, which is preceded by a 32-amino acid residue signal peptide. The two clones, whose molecular masses correspond to the two transcripts observed in murine L929 fibroblasts, contain 3' untranslated regions that are markedly different in sequence and length. Both clones can be expressed in COS cells and the recombinant protein is active in a mouse bone marrow colony assay.
Ladner et al. (Thu,) studied this question.