Amino-terminal amino acid sequence of murine colony-stimulating factor 1

We report the amino acid composition, the NH2-terminal sequence, and the tryptic map by HPLC for murine L-cell colony-stimulating factor 1 (CSF-1). CSF-1 purified by affinity chromatography was S-carboxymethylated under denaturing conditions and subjected to sequence microanalysis. CSF-1 contains four or five cysteine residues per subunit and approximately 30-40% carbohydrate by weight. Three contiguous cysteine residues were located in the NH2-terminal sequence. An additional two cysteine residues were located on the tryptic map. Previous studies as well as immunoblotting studies reported here suggest that sulfhydryl bridging plays a major role in maintaining the conformation of the protein. Carbohydrate was located on two tryptic fragments. The findings of a single NH2-terminal sequence in high yield and a relatively simple tryptic map (15 major peptides) suggest that CSF-1 contains two identical subunits. The NH2-terminal sequence of CSF-1 has only limited homology to insulin or insulin-like hormones but no homology with granulocyte/macrophage-CSF or interleukin 3.