He developed a biochemical system to study DNA replication-coupled chromatin assembly in a test tube and discovered proteins such as Chromatin Assembly Factor-1 (CAF-1) that cooperate with the DNA replication machinery to assemble new histones onto the DNA.
Two molecules of each of the four core histones (H2A, H2B, H3, and H4) form an octamer, around which approximately 146 bp of DNA is wrapped in repeating units, called nucleosomes.
Histones are globular proteins with a flexible N-terminus (taken to be the tail) that protrudes from the nucleosome.
He is well known as the discoverer of archaea histones, small DNA-binding proteins which are the precursors of histones in eukaryotes, as evidenced by his many published articles.