In eukaryotic cells, the organization of genomic DNA into chromatin regulates 
many biological processes, from the control of gene expression to the regulation 
of chromosome segregation. The proper maintenance of this structure upon cell 
division is therefore of prime importance during development for the maintenance 
of cell identity and genome stability. The chromatin assembly factor 1 (CAF-1) 
is involved in the assembly of H3-H4 histone dimers on newly synthesized DNA and 
in the maintenance of a higher order structure, the heterochromatin, through an 
interaction of its large subunit with the heterochromatin protein HP1a. We 
identify here a conserved domain in the large subunit of the CAF-1 complex 
required for its interaction with HP1a in the Drosophila fruit fly. Functional 
analysis reveals that this domain is dispensable for viability but participates 
in two processes involving heterochromatin: position-effect variegation and long 
range chromosomal interactions during meiotic prophase. Importantly, the 
identification in the large subunit of CAF-1 of a domain required for its 
interaction with HP1 allows the separation of its functions in 
heterochromatin-related processes from its function in the assembly of H3-H4 
dimers onto newly synthesized DNA.