Sheena D'Arcy

Seminar Details

Host: Dr. Tatyana Igumenova

Time: 4:00 pm- 5:00 pm

Location: BICH 108

Seminar Abstract

Asf1 is a histone H3-H4 chaperone and activator of the histone acetyltransferase Rtt109. The core domain of Asf1 has been extensively studied in vitro and is sufficient to bind H3-H4. Most in vitro studies of yeast Asf1 use a truncated construct that lacks a sizable C-terminal domain (CTD). This CTD accounts for 50% of Asf1, is poorly conserved, and exhibits signatures of disorder, including more than 50% acidic residues. ​​​​​​​We assessed the role of the Asf1 CTD in regulating Rtt109 using various biophysical and biochemical approaches, including hydrogen-deuterium exchange coupled with mass spectrometry. We compared full-length Asf1 to the typically used truncated, core-only Asf1 from Saccharomyces cerevisiae (res. 1-279 versus 1-169, respectively). We showed that including the CTD enhances binding to H3-H4, although stable interactions between the CTD and H3-H4 were not detected. We further uncovered a mechanism where interactions between the Asf1 CTD and H3-H4 preclude an exogenous interface between the Asf1 histone-binding domain and the Rtt109 C-terminal tail. In the Rtt109 complex, this reduces the kinetic stability of Asf1-(H3-H4) and weakens its interactions with Vps75-Rtt109, ultimately leading to promiscuous acetylation of H3-H4.  Our work highlights the functional significance of the Asf1 CTD and demonstrates how acidic stretches regulate the incorporation of PTMs. Our unprecedented mechanism suggests that the Asf1 CTD is tunable in regulating Rtt109 specificity and provides an impetus for future studies on disordered regions that make a small contribution to direct histone binding.