Transformation of chick-embryo fibroblasts by wild-type and temperature-sensitive Rous sarcoma virus alters adenylate...

The activity of the enzyme adenylate cyclase, a component of the plasma membrane, has been determined in chick-embryo fibroblasts and in cells transformed by either Bryan high-titer strain of Rous sarcoma virus (RSV-BH) or a temperature-sensitive mutant of this virus (RSV-BH-Ta). Adenylate cyclase activity is reduced in cells transformed by the wild-type virus and also by the temperature-sensitive mutant when the cells are grown at the permissive temperature (37 degrees ). Transformation results in an altered affinity (K(m)) for the substrate (Mg ATP). The apparent K(m) ATP is 0.23 mM in normal cells and 1.1 mM in cells transformed with wild-type virus. The K(m) ATP of the cells infected with RSV-BH-Ta is 0.67-1.0 mM at 37 degrees and 0.28 mM at 42 degrees . The enzyme from normal cells appears to have two binding sites for Mg(++), one at the catalytic site and a second at a regulatory site. Transformation by RSV-BH or RSV-BH-Ta (37 degrees ) apparently alters this second Mg(++) site. A decrease in adenylate cyclase activity occurs within 10 min after cells infected with RSV-BH-Ta are shifted from 42 degrees to 37 degrees ; the activity falls to one-half that of normal cells 30 min after the temperature shift. Our observations indicate that a viral function lowers cyclic AMP content by lowering the activity of adenylate cyclase, probably through some modification of the plasma membrane.