MOLECULAR HETEROGENEITY IN THE MAJOR URINARY PROTEINS OF THE HOUSE MOUSE MUS MUSCULUS

Major Urinary Proteins (MUPs) from different inbred strains of mouse h ave been analysed by high-resolution ion-exchange chromatography and m ass spectrometry. MUPs from six strains were resolved chromatographica lly into four major protein peaks which characterized two distinct phe notypes, typified by the profiles obtained from the Balb/c and C57BL/6 inbred strains. A combination of ion-exchange chromatography and elec trospray ionization mass spectrometry analysis of the MUPs from each s train identified five proteins, only one of which was common to both s trains. The charge and mass data, together with N-terminal sequence an alyses, were correlated with the masses of the proteins inferred from published cDNA sequences. Several members of the family of MUP sequenc es differ in only four positions, and in some circumstances the substi tutions elicit a minimal change in protein mass (Lys/Gln; Lys/Glu). Pe ptide mapping with endopeptidase Lys-C, followed by matrix-assisted la ser desorption ionization-time-of-flight mass spectrometry permitted i dentification of new MUPs that were correlated with partial cDNA seque nce data. In the two strains there are at least 13 different MUPs, eit her observed or predicted, indicating the heterogeneity of expression of this group of proteins.