Malaria is one of the most pervasive and destructive of all infectious diseases transmitted by mosquitos. About 300 million people worldwide are infected by malaria, which results in upward of a million deaths every year. The causative agents of malaria are protozoan parasites of the genus Plasmodium. The surface antigen is encoded by the var gene family, which consists of about 60 genes whose DNA sequences vary slightly. Expression of the type of var protein is known to change continuously, which allows parasites to evade the immune system. The var genes are located near the telomeres that are typically in heterochromatin state. The studies from 2006 revealed that the var genes are expressed when chromatin structure is disrupted via chemical changes in the histone proteins. Which of the following may serve as a plausible explanation that links var gene expression to chromatin changes?