Histone chaperones, a supporting role in the limelight

In eukaryotic cells, highly basic histone proteins are associated with the DNA to form the nucleosome, the fundamental unit of chromatin. Histories are closely escorted by historic chaperones from their point of synthesis up to their delivery site. We will present an overview of the historic chaperones identified to date with their various roles, in an attempt to highlight their importance in cellular metabolism. Nucleoplasmin will illustrate a role in historic storage and Nap-1, a historic translocator. CAF-1 and Hira will provide examples of distinct histone deposition factors coupled to and uncoupled from DNA synthesis, respectively, while Asf1 could act as a historic donor. We then will illustrate with two examples how histone chaperones can be associated with chromatin remodeling activities. Finally, we will discuss how the RbAp46/48 proteins, as escort factors, are part of multiple complexes with various functions. Based on these examples, we will propose a scheme in which the diverse roles of histone chaperones are integrated within an assembly line for chromatin formation and regulation. Finally, we discuss how these chaperones may have more than a supporting role in a historic metabolic pathway. (C) 2004 Elsevier B.V.