Catalyzes the ATP-dependent ligation of glycine to the 3'-end of its cognate tRNA, via the formation of an aminoacyl-adenylate intermediate (Gly-AMP) (PubMed:23816885). Also produces diadenosine tetraphosphate (Ap4A), a universal pleiotropic signaling molecule needed for cell regulation pathways, by direct condensation of 2 ATPs. Thereby, may play a special role in Ap4A homeostasis (By similarity). ATP + glycine + tRNA(Gly) = AMP + diphosphate + glycyl-tRNA(Gly) 2 ATP + H(+) = diphosphate + P(1),P(4)-bis(5'-adenosyl) tetraphosphate kcat is 0.38 sec(-1) for the aminoacylation reaction (at 25 degrees Celsius). Homodimer. Present with 98400 molecules/cell in log phase SD medium. Produced by alternative initiation at an upstream UUG codon in-frame of the first AUG used for isoform Cytoplasmic. Belongs to the class-II aminoacyl-tRNA synthetase family. GRS1, which appears to be a duplication of GRS2, is necessary and sufficient for both mitochondrial and cytoplasmic glycyl-tRNA synthetase activities, suggesting that GRS2 may not be essential. Truncated N-terminus. Truncated N-terminus. Truncated N-terminus.