Synthesis of A DNA binding protein in normal and transformed cells

The synthesis of a single‐stranded DNA binding protein (P8) by normal and Kirsten sarcoma‐virus‐transformed mouse cells was measured in serum depleted of growth factors by 3T3/B cells. P8 protein was made by the transformed but not the normal cells and was present during the time of peak DNA synthesis. Normal 3T3/B cells were partially synchronized by growth in depleted serum and a change to regular medium. Following the medium change the rate of DNA synthesis increased to a peak between 15 and 20 h and then fell. P8 protein synthesis coincided with the initiation of DNA synthesis and peaked during the same time period. When aminopterin was added to block DNA synthesis, P8 protein was still made during the period of normal DNA synthesis.