Investigating Protamine-Induced Toroid Formation*

In somatic cells, DNA is folded by histones, forming chromatin. However, protamine, a small, arginine-rich protein that allows DNA to fold in mammalian sperm cells. Protamine allows DNA to form loops, which are then condensed into toroids that are stacked within the sperm cell. In order to investigate protamine-induced toroid formation in DNA, we performed a tethered particle motion (TPM) assay. Due to the fact that we see multiple states present in our visualizations of standard deviation over time, toroid formation in DNA due to the binding of protamine is a multi-step process. Understanding how DNA folds has applications in biomaterials, epigenetics and infertility.