Fig. 5. S1 fibers are unrelated to cell proliferation and cellular metabolic activity. (A) RNA and DNA synthesis activities. ARL cells cultured to a 50-60% confluency (low density cells) or for 1 and 3 weeks at full confluency were incubated for 45 minutes in a fresh medium containing [³H]uridine or [³H]thymidine. Incorporated radioactivities were determined with respect to DNA, and compared with the low density cell values (100%). (B) ARL cells at about 20% confluency were further incubated for 3 days in the presence or absence of 20 µg/ml aphidicolin (aphid) or 6 mM hydroxyurea (HU) and stained with McAb 351. (C) ARL cells grown in complete medium were rinsed three times with serum-free medium, and further incubated for 75 hours in the presence (+) or absence (–) of 10% fetal calf serum. Cells were stained with McAb 351. Bar, 50 µm.