Abstract
A structural component of mitotic chromosomes that partially explains the compaction of DNA within mitotic chromosomes is suggested on the basis of the occurrence of long, regular cylindrical structures in preparations of isolated human chromosomes. These structures, "unit fibers", of a rather constant diameter of about 4,000 A have been postulated to be formed by coiling of the 250-300 A solenoid chromatin fiber that itself is formed by coiling of the 100 A string of nucleosome fiber. The human chromatid would thus be composed by a hierarchy of helices with contraction ratios for DNA at each level of coiling of 7 (string of nucleosomes), 5 (solenoid) and 40 (4,000 A "unit fiber" or "super-solenoid") which results in an overall contraction ratio for DNA in the "unit fiber" structures of about 1,400, which is approximately 5-fold less than the final contraction of DNA in intact chromatids of condensed metaphase chromosomes. The present report concerns more detailed studies with respect to the dimensions and cytochemical properties of the "unit fiber" structures observed in preparations of isolated human mitotic chromosomes that provide direct and indirect evidence in support of their "super-solenoid" structure and relate to known properties of human mitotic chromosomes.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
