Molecular cloning of a novel myeloid granule protein

AbstractGranulocytes are recognized by the presence of granules, including primary (azurophilic) and secondary types. Each granule ype contains distinct and characteristic families of enzymes. We have secreened a murine bone marrow cDNA library to obtain a series of sequences corresponding to mRNAs which are both myeloid‐specific and appear to be expressed only in immature bone marrow cells. A 1, 160 bp sequence (B9) has been isolated which shows restricted expression in murine bone marrow, with the highest levels in cultures enriched for promyelocytes. Translation yields a single open reading frame of 167 amino acids and a calculated MW of 19.33 kd. A single potential N‐glycosylation site is present. Evaluatin of the amino terminal sequence shows 2 polar amino acids flanking a hydrophobic region, suggesting a signal sequence and possibility of post‐translational modification. An extensive search of the protein data base reveals 30% identity over 90 amino acids with porcine cathelin, a cystain‐like systeine proteinase inhibitor. This sequence identity includes conservation of the 4 cysteine residues noted in all members of the cystain superfamily. In an attempt to further character