Increased satellite association induced by 5' bromodeoxyuridine treatment of phytohemaglutinin-stimulated blood lymphocytes.

5'-Bromodeoxyuridine (BrdU) present in the course of late S and G2 phases of the cell cycle in PHA-stimulated human lymphocyte cultures causes the despiralization and elongation of some chromosome regions, including short arms of acrocentric chromosomes. BrdU present at a concentration of 250 microM during the last 10 h in lymphocyte cultures from 19 healthy subjects did not affect the number of silver-stained NORs, but raised significantly the number of satellite associations of acrocentric chromosomes. The mere substitution of thymine by BrdU in DNA strands as a reason for increased number of satellite associations seems a less plausible explanation than the modification of DNA-protein complexes of NOR regions, which could alter the degree of their spiralization and cause the increased tendency of acrocentric chromosomes to associate in the subsequent metaphase.