Adenosine 3', 5'-monophosphate (cAMP) binding proteins from mouse neuroblastoma cells were purified by cAMP-affinity Sepharose resin and were analyzed by two-dimensional polyacrylamide gel electrophoresis. The two cAMP binding proteins R1 and R2 were identified on the second-dimensional slab gels. The isoelectric points of these proteins are 5.4 (Rl) and 5.2 (R2) and both proteins have a molecular weight of 48 000-50000. These two cAMP binding proteins, identified in the cellular fractions by the photoaffinity labeling techniques, are located above actin (pI = 5.4 and 43 000 Mr) on the second-dimensional slab gels. Analysis of cellular fractions, cytoplasmic, particulate and nuclear nonhistone proteins, from [35S]methionine-labeled cells on two-dimensional gels, shows the presence of two cAMP binding proteins, R1 and R2. N6, O2'-Dibutyryladenosine 3',5'-monophosphate (Bt2cAMP) induced only one cAMP binding protein, Rl, from three- to eightfold in these fractions. Bt2cAMP stimulated the synthesis of cAMP binding protein Rl without affecting R2. cAMP binding protein R1 is 0.06 and 0.2% of the total cytoplasmic proteins in the control and Bt2cAMP treated cells and R2 is 0.06% in both cells. Chromatin isolated from Bt2cAMP treated cells also showed an increase in [3H]cAMP binding. Bt2cAMP also affected the levels of 42 nuclear nonhistone proteins: 23 proteins increased and 19 proteins decreased. The increase in the nuclear cAMP binding protein and the changes in other nonhistone proteins may affect the transcriptional activity of some specific genes, thus causing biochemical changes in neuroblastoma cells.
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