The nucleosome is composed of 145 base pairs of double-stranded DNA wrapped around a central core of 8 histones – 2 each of: H2A, H2B, H3, and H4. The N-terminus of each histone has many positively-charged amino acids that interact with the negatively-charged phosphate groups of the DNA backbone.
This 3-D structure reveals that histones interact only with the minor groove of DNA. The major groove is then available for sequence-specific DNA binding proteins, such as Zif 268. (See Zinc Finger Mini Model.) It can be used to demonstrate how DNA is arranged and packaged in the nucleus, and initiate discussions about how the DNA is accessed by transcription factors and other regulatory elements. Each histone is shown in spacefill format and in a different color: H2A is yellow, H2B is red, H3 is blue, and H4 is green. The DNA backbone is shown in white. The DNA base pairs are displayed as white hydrogen bonds.
The 1910 Nobel Prize in Physiology or Medicine was awarded to Albrecht Kossel "in recognition of the contributions to our knowledge of cell chemistry made through his work on proteins, including the nucleic substances". (In 1896 he discovered histidine, then worked out the classical method for the quantitaive separation of the hexone bases.)
The 1982 Nobel Prize in Chemistry was awarded to Aaron Klug "for his development of crystallographic electron microscopy and his structural elucidation of biologically important nucleic acid-protein complexes".
Molecule of the Month
The Molecule of the Month by scientist, author and artist Dr. David Goodsell includes an introduction to the structure and function of the chosen molecule and a discussion of its relevance to human health and welfare. Molecule of the Month articles are frequently referred to by teachers, students and researchers. More...