CLONING AND CHARACTERIZATION OF MOUSE LMP3 CDNA, ENCODING A PROTEASOME BETA-SUBUNIT

We isolated and sequenced a cDNA encoding mouse proteasome subunit LMP 3 from a macrophage cDNA library. The gene encodes a 264-amino-acid pr otein with a calculated molecular mass of 29.11 kDa and an isoelectric point (pI) of 5.44. Comparison of the predicted protein sequence with that of the human and rat homologues, N3, revealed 11 and eight chang es, respectively, in the cleaved NH2-terminal presequence of the precu rsor protein (pre-LMP3), and six and 10 changes, respectively, in the processed product. To corroborate the predicted molecular mass and pI, we analyzed LMP3 by immunoprecipitation with a mAb to human N3 that c rossreacts with mouse LMP3. Precursor and processed forms of LMP3 were identified by 2D NEPHGE-PAGE, and their mobilities suggest the Lmp3 c lone encodes the entire protein sequence. (C) Elsevier Science B.V.