WD dipeptide motifs of the p48 subunit of chromatin assembly factor-1 is essential for viability of DT40 chicken B cell line

Chromatin assembly factor-1 (CAF-1) is involved in chromatin assembly and comprises three subunits, p48, p60 and p150. The p48 subunit, CAF-1p48 (p48), with seven WD (Trp-Asp) repeat motifs, is a member of the WD protein family. The immunoprecipitation experiment revealed that ßpropeller structure of p48 was less stringent for its binding to HDAC1, but more stringent for its binding to both histone H4 and p60, indicating that the proper ß-propeller structure of p48 is essential for the binding to these two proteins. Complementation experiments, involving missense and truncated mutants of FLAG-tagged p48, revealed that mutations of every of seven WD dipeptide motifs, like both the N-terminal and C-terminal truncated mutations, could not rescue for the tetinduced lethality. These results indicate not only that p48 is essential for the viability of vertebrate cells, although the yeast p48 homolog is nonessential, but also that all the seven WD dipeptide motifs are necessary for the maintenance of the proper structure of p48 that is fundamentally important for its functions.