Publisher Summary This chapter discusses the recent studies in order to draw a contemporary picture of the structure of transcribing chromatin. The basic structure of “active” chromatin, unique, repeating, altered nucleosomal structure, is discussed in this chapter. Both micrococcal nuclease and DNase II digestion studies strongly suggest that “active” chromatin is organized in repeating subunits that share at least some properties, with bulk nucleosomes. Isolation of pure chromatin fragments containing “active” ribosomal and nonribosomal genes and careful studies of their composition and organization are required before understanding the basis for the variability of “active” chromatin structure. From the conflicting results available at the present time, it is obviously impossible to conclude whether or not histone H1 (and its variants) is present in “active” chromatin. Again, there is a need for careful well-controlled studies and again, the use of antibodies directed against the various H1 variants should be very useful in elucidating whether they are associated with the isolated “active” subunits. as they are with the isolated nucleosomes of bulk chromatin.
