novobiocin and hydroxymethyltrioxsalen

We have used a DNA crosslinking assay to measure intercalation of the psoralen derivative HMT (4'-hydroxymethyl-4,5',8-trimethylpsoralen) into barley (Hordeum vulgare) plastid chromosomal DNA during chloroplast and etioplast development. Intercalation into DNA in intact plastids in vivo and in plastid lysates in vitro shows that chromosomal DNA in the most mature chloroplasts intercalates HMT less efficiently than DNA in younger chloroplasts. In contrast, there is no change in HMT intercalation during etioplast differentiation in the dark. Our results also show that DNA in higher plant plastid chromosomes is under superhelical tension in vivo. The lower susceptibility to HMT intercalation of DNA in the most mature chloroplasts indicates that late during chloroplast development the superhelical tension or the binding of proteins to the DNA or both change.

Topics: Blotting, Southern; Chloroplasts; Chromosomes; Cross-Linking Reagents; DNA; Hordeum; Intercalating Agents; Novobiocin; Plasmids; Trioxsalen

We have analyzed changes in the structure of chloroplast chromosomes in response to light in growing Chlamydomonas cells using a crosslinking assay based on the intercalation of HMT (4'-hydroxymethyl-4,5',8-trimethylpsoralen) into DNA. Our results show that the structure of chloroplast chromosomes in at least three widely separated regions is different in light-grown vs. dark-grown cells. Structural changes in chloroplast chromosomes occur within 3 hrs after exposure to light or darkness, respectively. The response to light is not inhibited by atrazine and can be elicited by dim blue light incapable of evolving O2, indicating that it does not require photosynthesis. Inhibition of cytoplasmic protein synthesis with cycloheximide prevents this response to light, indicating that it depends, at least in part, on proteins imported from the cytoplasm.

Topics: Atrazine; Chlamydomonas; Chloroplasts; Chromosomes; Cross-Linking Reagents; Cycloheximide; DNA; Gamma Rays; Light; Nalidixic Acid; Novobiocin; Photosynthesis; Plant Proteins; Trioxsalen