Evidence for DNA polymorphism in vivo: laser Raman microsopy of chromosomes in the single eukaryotic cells--comparison with model systems

There is now definitive evidence from Raman and X-ray studies that DNA in a relaxed condition in aqueous solution is in the standard B type conformation. On the other hand, DNA in crystals, in concentrated salt solutions and bound to proteins can exist in other configurations. The question arises: what is the structure of DNA in the nucleus of a living cell where its long length must be subjected to repeated folds in order to pack it into such a small space? To answer this question we designed and built a laser Raman microscope to take the Raman spectra of DNA in the packaged state in which it occurs in nature. Spectra have been taken of the DNA in salmon sperm, squid sperm, and the nucleus of the salivary gland of drosophila melanogaster. The majority of the deoxynucleotide residues in the DNA in the nucleus belongs to the B-type family of conformations. However, the DNA in the nucleus may have a different furanose ring pucker than it does in solution.