Acts as a component of chromatin assembly factor 1 (CAF-1), which assembles histone octamers onto replicating DNA in vitro. It performs the first step of the nucleosome assembly process, bringing newly synthesized histones H3 and H4 to replicating DNA; histones H2A/H2B can bind to this chromatin precursor subsequent to DNA replication to complete the histone octamer. p50 and p60 form complexes with newly synthesized histones H3 and acetylated H4 in cell extracts (By similarity). Independently, MSI1 is involved in regulation of the RAS/cAMP pathway via sequestration of NPR1. Interacts with protein kinase NPR1 (PubMed:11238915). Component of chromatin assembly factor 1 (CAF-1), which is composed of MSI1/p50, CAC2/p60 and CAC1/p90 (PubMed:11238915). Interacts with RTT106 (PubMed:19683497). Present with 149 molecules/cell in log phase SD medium. Belongs to the WD repeat RBAP46/RBAP48/MSI1 family.