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Discussion of Paper

DR. MAX HOMMERSAND (University of North Carolina, Chapel Hill, N . C . ) : I have seen reports on Dodge’s studies of proteins in the nucleus outside the chromosomal material which consists of DNA fibrils. I wonder if that protein

Leedale: Phylogenetic Aspects of Nuclear Cytology 453

has been identified and whether it is histone. Or is histone absent in the dino- flagellate nuclei?

DR. LEEDALE: I don’t want to quote Dodge before he publishes, but I think that he has found no evidence of histone protein in the nucleus. There is cer- tainly no protein of any sort associated with the chromosomes, and almost no histone protein in the nucleus.

DR. C. PETER WOLK (Michigan State University, East Lansing, Mich.) : Has histone been looked for in Euglena?

DR. LEEDALE: It has and it is present. The chromosomes in Euglena have DNA and histone protein and show none of the special organization which is present in the dinoflagellate chromosome. There appears to be no close rela- tionship between the two types of chromosomes.

DR. 0. BROWN (University of North Carolina, Chapel Hill, N . C . ) : I have a question that might relate to this: In euglenoids you have found some endo- nuclear bacteria. ?s it possible that these may be considered as really bacterial, or perhaps a manifestation of the organization of the nuclear material? Could this be a type of isolation of nuclear material?

DR. LEEDALE: They almost certainly are bacteria. I t is an interesting situa- tion that some strains of Euglena contain a bacterial population which lives inside the nucleus. We have a situation in which the membrane systems in the cytoplasm contain bacterial-size ribosomes, with a DNA center, and they are also inside the nucleus. I think that since one can get strains of the same Euglena (some with and some without these organisms), and since all the chemical and structural evidence suggests that these are really bacterial cells, at this stage it would be somewhat far fetched to suggest that the structures are manifestations of the chromosomes.