Molecular organization of DNA in chromosomes

✍ Scribed by Samarendra Basu

• Publisher: Wiley (John Wiley & Sons)
• Year: 1977
• Tongue: English
• Weight: 886 KB
• Volume: 16
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1977.360161016

✦ Synopsis

Abstract

Metaphase chromosomes of Chinese hamster and lampbrush chromosomes of Triturus viridescens were studied for DNA arrangement by polarized fluorescence microscopy and by linear dichroic ratio measurements. Intact chromosomes showed a small but negative polarization (−8%) of fluorescence, while the dichroic ratio was negative and quite appreciable (0.85). On treatment with trypsin or RNase the polarization value increased to about −34% with no change in the polarization direction. The dichroic ratio on the other hand remained unchanged on such enzyme treatments. These results, along with the data of form dichroism and the change in fluorescence color following any enzyme action, suggest that basically the preexisting DNA arrangement was revealed by these enzymes. The fully enzyme‐treated chromosome–dye complexes showed cross‐bands. Quantitatively, the highest degree of DNA orientation across the above two chromosomes was in the range of 15–34%. This orientation fits well with a coiled coil‐DNA, which is mostly longitudinal in these chromosomes. It is suggested that this longitudinal coil may have occasional defects in DNA structure. Alternatively, this coil may terminate into regions of random DNA and unsupercoiled DNA showing lateral projections, such as loops. This alternating feature of the DNA arrangement would tandemly repeat in either metaphase and lampbrush chromosomes.