Figure 1. Structure and function of the Atg13 HORMA domain. (A) The Atg1 complex initiates autophagy at the PAS, shown here as marked by Atg13-GFP. (B) Schematic of the Atg1 complex highlighting the context of the HORMA domain. The Atg1 complex is a dimer of pentamers, with just one pentamer shown here for simplicity. (C) Space filling model of the Atg13 HORMA domain, with the bound sulfate ion shown as a marker for a likely biological phosphate binding site. Note the prominent peptide-sized groove running southwest to northeast. EAT, early autophagy targeting/tethering; NTD, N-terminal domain. Adapted from Jao CC, Ragusa MJ, Stanley RE, Hurley JH. A HORMA domain in Atg13 mediates PI 3-kinase recruitment in autophagy. Proc Natl Acad Sci U S A 2013; 110:5486–91; PMID:23509291; 10.1073/pnas.1220306110.