Fig. 1.

Inheritance at the replication fork. a The Naked DNA Paradigm: although the classical semi-conservative model of DNA duplication is useful for explaining Mendelian genetics, the model of DNA in isolation is imperfect for most nuclear processes that require the cooperation of DNA with nuclear proteins, such as inheritance during S-phase, which requires more than just passing a gene to daughter cells. This model simply shows DNA strands unwound at the replication fork by helicase, which is followed by the leading and lagging strands of DNA replication by DNA polymerase. b A modern model for inheritance: the more complete model of inheritance, which includes the DNA along with chromatin. At the replication fork, nucleosomes are disrupted to provide access to the DNA polymerase for DNA duplication. These displaced parental histones (shaded green-purple) are reassembled after fork passage with the assistance of chaperone proteins, such as ASF1. In addition, new histones (purple) are required to fully reconstitute chromatin on the two daughter strands, which is also facilitated by chaperone proteins, including ASF1 and CAF-1. New histones acquire marks in accordance to the pattern carried by the parental histones to inherit gene expression states