Inhibition of DNA synthesis of synchronized RSa cells by human leukocyte interferon

A human leukocyte interferon preparation suppressed DNA synthesis and subsequent mitosis of synchronously growing virus-transformed human RSa cells. DNA synthesis was inhibited completely when interferon was added to cell cultures in late G1 phase, but was not so inhibited when interferon was added in G1/S boundary phase. Overall protein synthesis was reduced only slightly by interferon treatment. The findings suggested that critical events leading to the inhibition of DNA synthesis and subsequent mitosis by interferon action take place in late G1 phase or S phase.