The histone with which DNA is complexed in the genetic material of higher organisms has as one of its roles the regulation of DNA-dependent RNA synthesis.'-3 DNA fully complexed with an appropriate histone is not transcribed by RNA polymerase. For the deeper understanding of this regulation it is necessary to know whether it is reversible; whether in life a histone molecule once complexed to the DNA template can dissociate again. The present paper is addressed to this point. The experimental strategy consists in determining whether histone molecules of the chromosomal nucleohistone complex are replaced by freshly synthesized ones in cells in which there is no replication of DNA and hence no requirement for net de novo synthesis of histone. It will be shown that histones may be divided into two classes, those which are replaced (turnover) in cells in which DNA is not replicating, and those of the alternative class which do not turn over at all. The latter are synthesized only during, and in fact are dependent upon, DNA replication.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.