Synthesis of chromosomal proteins and Epstein-Barr virus DNA in activated burkitt somatic cell hybrids

Abstract

A Burkitt somatic cell hybrid line, D98/HR-1, contains a latent Epstein-Barr virus (EBV) genome which can be induced into expression by 5-iodo-2′-deoxyuridine (IUdR). Synthesis of chromosomal proteins under the conditions which induced EBV DNA replication was studied. Maximum DNA synthesis in IUdR-treated cells occurred 3 hr after transfer of the cells to IUdR-free medium in contrast to 6 hr in untreated cells. However, fourfold more DNA was synthesized in the untreated cells. About 80% of the DNA synthesized in IUdR-treated cells was identified as viral DNA with a density of 1.718 g/cm 3 by EBV-specific cRNA-DNA hybridization. The synthesis of viral DNA in IUdR-treated cells was inhibited by Acyclovir (ACV) [9-(2-hydroxyethoxymethyl)guanine] whereas in untreated cells DNA synthesis was not affected by this drug. Synthesis of total cellular proteins in cells not treated with IUdR increased sharply within an hour after transfer to fresh medium and kept increasing for 16 hr. Synthesis of chromosomal proteins in these cells followed the same kinetics as the synthesis of total cellular proteins. In contrast, synthesis of chromosomal proteins in IUdR-treated cells increased selectively while there was no significant increase in total cellular protein synthesis 3 hr after release from IUdR. Electrophoretic analysis on polyacrylamide gels of the chromosomal proteins from IUdR-treated cells revealed that the synthesis of three polypeptides (130 × 10 3, 110 × 10 3, and 26 × 10 3 daltons) is selectively induced upon releasing the cells into IUdR-free medium. The dramatic increase in these three polypeptides when EBV DNA replication reaches its maximum and their failure to be synthesized in the presence of ACV suggest that these polypeptides may play some role in regulating the reactivation of latent EBV genomes.