CLONING OF A GENE ENCODING A HUMAN-LEUKOCYTE PROTEIN CHARACTERIZED BYEXTENSIVE HEPTAD REPEATS

Complementary DNA (cDNA) clones, encoding a fusion protein that was re cognised by an antiserum raised against a purified polypeptide fragmen t of a 180-kDa human leukocyte protein, were isolated from a lambda gt 11 expression library. The clones encoded a unique amino acid (aa) seq uence interspersed with heptad repeats that typify coiled-coil protein s, and hybridised to a 5-kb transcript universally expressed in a pane l of eight human tissues. Comparatively high levels of RNA expression were seen in testis, ovary and mitogen-activated peripheral blood leuk ocytes (PBLs). The deduced 1300-aa sequence reveals a protein with a t ypical signal peptide, a hydrophilic domain containing an N-terminal g lobular head with a nuclear localisation signal sequence, a C-terminal region of coiled-coil structure, a candidate transmembrane domain, an d a short 10-aa C-terminal domain. Rabbit polyclonal antisera raised a gainst a truncated lambda gt11 fusion protein recognised a 150-170-kDa protein (non-reduced) in mitogen-activated PBLs. The protein designat ed here as CG-1 may exist as a homodimer destined for translocation to the nucleus, with a role in leukocyte differentiation and/or effector function.