Synthesis of native 60S and 40S ribosomal subunits in Yoshida rat ascites hepatoma AH-130 cells: correlation with the rate of cell growth.

The 60Sn and 40Sn subunit ribosome synthesis declined significantly in Yoshida rat ascites hepatoma AH-130 cells from the log phase to the plateau phase of the in vivo growth. Two main classes of 40Sn particles with protein/RNA ratios of 1.82 (p2) and 1.20 (p3) and a minor "heavy" one with protein/RNA ratio of 0.96 (p1) could be distinguished reproducibly by their ultraviolet absorption after sucrose zone sedimentation. The p2 particles appeared the dominating class in log phase cells. In plateau phase cells a decrease of p2 and an increase of p3 particles was observed. Under these conditions the p1 particles and the peaks corresponding to 60Sn subunits and to 80S ribosomes were also increased. Newly synthetized 40Sn particles banded in the p3 region of the gradient and p2 particles originated from them. These particles entered into the ribosomal cycle and contained poly(A) RNA. Formation of radioactive 80S couples by subunits entering into the ribosomal cycle was markedly stimulated in log phase cells and almost completely blocked in cells at the plateau phase of growth.