In vivo study of the nucleosome assembly functions of ASF1 histone chaperones in human cells.
CEA
Histone chaperones have been implicated in nucleosome assembly and disassembly as well as histone modification. ASF1 is a highly conserved histone H3/H4 chaperone that synergizes in vitro with two other histone chaperones, CAF-1 and HIRA, in DNA-synthesis coupled and DNA-synthesis independent nucleosome assembly. Here, we identify mutants of histones H3.1 and H3.3 that are unable to interact with human ASF1A and ASF1B isoforms, but that are still competent for binding CAF-1 and HIRA respectively. We show that these mutants are defective in their efficient deposition into chromatin in vivo. Furthermore, we found that both ASF1A and ASF1B participate in the DNA-synthesis independent deposition of H3.3 in HeLa cells, thus highlighting an unexpected role for ASF1B in this pathway. This pathway does not require interaction of ASF1 with HIRA. Altogether, we provide the first direct determination of a role of ASF1A and ASF1B in the efficiency of nucleosome assembly in vivo in human cells.
