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A study was made of the in vitro phosphorylation of some nucleosides in cell-free extracts from a thioguanine-resistant subline of Ehrlich ascites carcinoma which lacked inosine monophosphate – guanosine monophosphate pyrophosphorylase. The results indicated that there were kinases which catalyzed the phosphorylation of a variety of nucleosides. Ribofuranosyl-6-thiopurme was phosphorylated whereas the xylofuranosyl-, arabinofuranosyl-, and lyxofuranosyl-6-thiopurine were not substrates. The xylose and ribose derivatives of 6-methylthiopurine were phosphorylated but the arabinose derivative was not. Guanosine and some of its analogs were also phosphorylated but no correlation could be found between structure and phosphorylation of the guanosine analogs tested.The reaction showed dependence on the addition of divalent cation and an ATP-regenerating system.

DNA-mediated gene transfer was used to evaluate the cause and effect relationship between mutations in cAMP-dependent protein kinase activity and cellular resistance of adrenocortical tumor cells to ACTH and cAMP. Protein kinase defective, Kin 8 adrenocortical tumor cells were transformed with genomic DNA from an ACTH- and cAMP-responsive adrenocortical cell line and screened for the recovery of morphological responses to the cAMP analog 8-bromo-cAMP (8BrcAMP). 8BrcAMP-responsive transformants were recovered with a frequency of approximately 0.5 per 103 transformation-competent cells. These transformants recovered the ability to round up in the presence of ACTH and were able to respond to both ACTH and 8BrcAMP with increased steroidogenesis. They also recovered cAMP-dependent protein kinase activity. The transformants, however, were unstable and concomitantly lost cAMP-dependent protein kinase activity and steroidogenic and morphological responses to ACTH and 8BrcAMP. These observations suggest that a single gene, probably the gene encoding the regulatory subunit of cAMP-dependent protein kinase, is responsible for the resistance of the Kin 8 mutant to ACTH and cAMP.