MULTIPLE FORMS OF THE G-PROTEIN-RELATED BETA-SUBUNIT IN DAUDI LYMPHOBLASTOID-CELLS

We have explored the forms of the G protein-related beta subunit which are present in Daudi lymphoblastoid cells. Northern blotting with lab eled beta-1 and beta-2 probes indicates that two messages of 3.3 kb an d 1.7 kb are present for both beta-1 and beta-2, implying that multipl e forms of the beta subunit are present. Antibodies were raised agains t two peptides of the beta subunit (residues 1-23 and 127-145). Both a ntibodies detected subunits at 35 kDa and 31 kDa, of which the 35-kDa form predominates in the membrane fraction and the 31-kDa one in the c ell cytosol. Crosslinking of the membrane fraction with the cleavable crosslinker (DTSSP) caused a simultaneous diminution in the 31-kDa for m while increasing the amount of the 35-kDa form - a pattern which was reversed upon the reduction of these crosslinks with DTT. Studies of the soluble form indicate that this is truly a soluble protein since c entrifugation at 200 000 x g for 2 h did not diminish the levels of th e protein in the soluble fraction. Sedimentation analysis indicates th at the soluble beta-homologue is found in fractions which overlap with those which contain the mu chain of immunoglobulin at a position clea rly distinct from the expected positions of free mu or free beta. Our results suggest that at least two forms of a subunit which is closely related to, or identical with, the beta subunit of G proteins are pres ent in Daudi cells.