GTPase involved in protein precursor import into chloroplasts. Seems to recognize chloroplast-destined precursor proteins and regulate their presentation to the translocation channel through GTP hydrolysis. Binds GTP, GDP, XTP, but not ATP. Probably specialized in the import of nuclear encoded photosynthetic preproteins from the cytoplasm to the chloroplast, especially during early development stages. Binds 1 Mg(2+) ion by subunit. Homodimer, heterodimer with TOC34 and TOC159, and monomer. The homodimerization and the dimerization with TOC159 require the binding of GTP on Arg-130, and a hypothetical coGAP factor. The dimeric form has a higher GTPase activity than the monomeric form. Part of the TOC core complex that includes 1 protein for the specific recognition of transit peptides surrounded by a ring composed of four proteins forming translocation channels, and four to five GTP-binding proteins providing energy. This core complex can interact with components of the TIC complex to form a larger import complex. Chloroplastic protein precursor such as prSS (precursor of the RuBisCO small subunit) interacts with these complexes. The TOC complex contains a specific subset of polar lipids such as digalactosyldiacylglyceride (DGDG), phosphatidylcholine (PC) and phosphatidylglycerol (PG). Interacts at least with TOC75-3. Forms large complexes including TOC33, pPORA and OEP161 during pPORA import into plastids at the plastid envelope membrane (PubMed:10998188, PubMed:12473690, PubMed:12951325, PubMed:15773849, PubMed:17337454, PubMed:18400179, PubMed:18541539). Interacts with SP1 (PubMed:23118188). May contain beta barrel transmembrane regions. Mostly expressed in seedlings and flowers, and, to a lower extent, in roots, stems, and leaves. Mostly expressed in photosynthetic tissues undergoing rapid growth. Observed in cotyledons and vascular tissues of hypocotyls of young seedling. In roots, restricted to apical and lateral meristems, and vascular bundles. In stems, mostly detected in the upper part. Expressed in young and middle-aged leaves. In flowers, confined to sepals. Up-regulated by CIA2 in leaves. Induced in light but repressed in darkness. Phosphorylated by a kinase present in the outer envelope of chloroplast. When Ser-181 is phosphorylated, the binding to preprotein, GTP and GDP is inhibited, and thus, GTPase activity is repressed. Plants exhibits a pale yellowish phenotype. Belongs to the TRAFAC class TrmE-Era-EngA-EngB-Septin-like GTPase superfamily. AIG1/Toc34/Toc159-like paraseptin GTPase family. TOC34 subfamily.