Identification of a new murine eosinophil major basic protein (mMBP) gene:cloning and characterization of mMBP-2

We have identified a new eosinophil major basic protein gene family member in the mouse and have given it the designation murine major basic protein-2 (mMBP-2), The gene was initially characterized as a unique expressed seque nce tag (EST) clone having significant identity to the previously recognize d member of this gene family, mMBP-1. The EST was used to screen and isolat e mMBP-2 from a bone marrow cDNA library. In addition, a genomic clone of m MBP-2 was isolated and this gene was shown to be physically hulled to withi n 100 kb of mMBP-1 on the central region of mouse chromosome 2. Progressive similarity alignment of the deduced mMBP-2 open reading frame demonstrates the apparent conservation of the "pre-pro-mature" protein structure found in the other known mammalian MBPs. Mature mMBP-2 maintains the cationic nat ure associated with these proteins with a predicted pI of 9.95. However, un like the human MBPs, which display a three orders of magnitude charge diffe rence [hMBP-1 (pI 11.4) vs. hMBP-2 (pI 8.7)], mMBP-2 is only slightly less cationic than mMBP-1 (pI 10.5), Expression studies demonstrate that transcr iption of the mMBP-2 gene parallels mMBP-1 and is confined to hematopoietic compartments engaged in eosinophilopoiesis. Moreover, using mMBP-1 knockou t mice and immunohistochemistry with an antisera that recognizes both mMBP- 1 and -2, we demonstrate that mMBP-2 protein expression is restricted to eo sinophil lineage-committed cells.