Purification of RNA-DNA hybrids by exclusion chromatography

Size-exclusion chromatography of DNA restriction fragments. Fragment length determinations and a comparison with the behaviour of proteins in size-exclusion chromatography

Size-exclusion chromatography of double-stranded DNA restriction fragments on Superose 6 is shown to be an accurate method for chain length determination of unknown DNA. Ionic interaction was observed between DNA and the gel matrix but was easily prevented by the addition of 0.15-0.2 M sodium chloride to the eluent. Compared to protein, the selectivity curve of DNA fragments was found to be steeper reflecting the different chromatographic behaviour of rod-like and globular molecules. The relationships between the selectivity curves of DNA and protein were similar on Superose 6 and on Sephacryl S-500.

Adenovirus early gene products may control viral mRNA accumulation and translation in vivo

The mechanisms controlling early adenovirus gene expression in vivo have been studied using inhibitors of protein synthesis. When inhibitors were added shortly before or at the onset of infection, viral mRNA from all early regions was transcribed, spliced and accumulated over a 7 hr period. After longer pretreatment, accumulation of several early mRNAs were suppressed. Addition of inhibitors 1 hr after infection enhanced the accumulation of viral mRNA in the cytoplasm. Translation of early mRNA selected on adenovirus DNA in a cell-free system reflected the amount of viral mRNA present. A viral coded product may therefore control accumulation of viral mRNA. A different pattern emerged when inhibitors of protein synthesis were removed at 5 hr postinfection and cells were removed at 5 hr postinfection and cells were pulse-labeled in vivo. If inhibitors were introduced at or before infection, early viral proteins were synthesized only after a lag of 1-3 hr. However, if treatment was introduced 1 hr postinfection, reversion of the protein synthesis block was instantaneous. It appears that protein synthesis inhibitors reveal an in vivo translational block for viral mRNA. This block could be overcome by preinfection with a related virus. Furthermore, no block was observed in a virus-transformed human embryonic kidney cell line (293) which expresses early region 1 of the viral genome. Viral gene product(s) encoded in early region 1 may control translation of early adenovirus messenger RNA in vivo.