The F3-F2a1 complex as a unit in the self-assembly of nucleoproteins

A specific and stable interaction between histones f3 and f2a1 was demonstrated to take place in the absence of DNA. When a mixture of these histones was subjected to velocity sedimentation under conditions in which the separate histones are aggregated and precipitate, the mixture of f3 and f2a1 remained soluble and these histones appeared to cotransport through the gradient, indicating the establishment of an isolatable, stable f3-f2a1 complex. This isolated complex subsequently binds to DNA quantitatively to form nucleohistone. Stoichiometry data strongly suggest that histones f3 and f2a1 bind to DNA as a unit; this is the only type of f2a1 binding to DNA that can take place under mild conditions. Histone f1 can act as a modifier of the f3-f2a1-DNA interactions by augmenting the formation of the f3-f2a1 complex and consequently enhancing the overall binding of these histones to DNA. No significant interactions of histones f2b and f2a2 with other histones could be demonstrated. Because of the findings reported here and the known affinity characteristics of the arginine-rich histones to DNA in native chromatin (in particular their stimultaneous extraction from chromatin by salt), we suggest that the (f3 + f2a1)-DNA complex is a structural component of native chromatin. We would also like to propose that, in vivo, histones may possess a considerable amount of quaternary structure, which would greatly increase the specificity of their role as potential regulators of the structure and function of the eucaryotic chromosomes.