Results obtained in a number of laboratories strongly suggest that the globin genes of avian reticulocytes are complexed with histones. The authors do not yet know whether the complement of histones, their extent of modification, or their detailed conformation is different from normal in the neighborhood of an actively transcribed gene, but, in any case, it appears that the transcription mechanism must contend with a nucleohistone complex. That the nucleosome need not be an insurmountable obstacle to polymerase is demonstrated by their transcription studies. The data show that, under suitable conditions, E. coli RNA polymerase is not greatly inhibited with respect to rate of propagation by the presence of the four core histones on the DNA. If the nucleosome were a static structure, it would be difficult to understand how the polymerase could maneuver past it. It seems likely, however, that the nucleosome is in some sense labile; it may undergo exchange to other DNA binding sites, it may slide, or it may open up to permit the function of the polymerase. Further investigation of the roles of the various histones in the folding of the nucleosome, of the energies involved in such conformational changes, and of the role of histone modification in altering these energies may help us the understand the biological behavior of the nucleosome in terms of its chemistry.
ASJC Scopus subject areas
- Molecular Biology