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 labeled beta-1 and beta-2 probes indicates that two messages of 3.3 kb and 1.7 kb are present for both beta-1 and beta-2, implying that multiple forms of the beta subunit are present. Antibodies were raised against two peptides of the beta subunit (residues 1-23 and 127-145). Both antibodies 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 cell cytosol. Crosslinking of the membrane fraction with the cleavable crosslinker (DTSSP) caused a simultaneous diminution in the 31-kDa form 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 centrifugation at 200,000 x g for 2 h did not diminish the levels of the protein in the soluble fraction. Sedimentation analysis indicates that the soluble beta-homologue is found in fractions which overlap with those which contain the mu chain of immunoglobulin at a position clearly 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 present in Daudi cells.
Lin
C K
CK
Regional Research Laboratory, Kaiser Permanente Medical Center, Los Angeles, California 90027.
Kaptein
J S
JS
Gu
D G
DG
Kalunta
C I
CI
Lad
P M
PM
D000595:Amino Acid Sequence; D000818:Animals; D001402:B-Lymphocytes / Q000378:metabolism*; D015152:Blotting, Northern; D002462:Cell Membrane / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000096:biosynthesis* / Q000737:chemistry; D008969:Molecular Sequence Data; D010641:Phenotype; D012333:RNA, Messenger / Q000032:analysis / Q000302:isolation & purification; D011817:Rabbits; D015398:Signal Transduction; D014407:Tumor Cells, Cultured
D012333:RNA, Messenger; D019204:GTP-Binding Proteins