The function of ATL1 (atlastin GTPase 1, Ensembl gene identifier ENSG00000198513) is as follows. Atlastin-1 (ATL1) is a membrane-anchored GTPase that mediates the GTP-dependent fusion of endoplasmic reticulum (ER) membranes, maintaining the continuous ER network. It facilitates the formation of three-way junctions where ER tubules intersect (PubMed:14506257, PubMed:18270207, PubMed:19665976, PubMed:27619977, PubMed:34817557, PubMed:38509071). Two atlastin-1 on neighboring ER tubules bind GTP and form loose homodimers through the GB1/RHD3-type G domains and 3HB regions. Upon GTP hydrolysis, the 3HB regions tighten, pulling the membranes together to drive their fusion. After fusion, the homodimer disassembles upon release of inorganic phosphate (Pi). Subsequently, GDP dissociates, resetting the monomers to a conformation ready for a new fusion cycle (PubMed:14506257, PubMed:21220294, PubMed:21368113, PubMed:23334294, PubMed:38509071). May also regulate more or less directly Golgi biogenesis (PubMed:17321752). Indirectly regulates axonal development (By similarity). {ECO:0000250|UniProtKB:Q6PST4, ECO:0000269|PubMed:14506257, ECO:0000269|PubMed:17321752, ECO:0000269|PubMed:18270207, ECO:0000269|PubMed:19665976, ECO:0000269|PubMed:21220294, ECO:0000269|PubMed:21368113, ECO:0000269|PubMed:23334294, ECO:0000269|PubMed:27619977, ECO:0000269|PubMed:34817557, ECO:0000269|PubMed:38509071}.