The function of ENSG00000235387 (SPAAR, small regulatory polypeptide of amino acid response) is as follows. [Isoform 2]: Negative regulator of amino acid sensing and mTORC1, a signaling complex promoting cell growth in response to growth factors, energy levels and amino acids (PubMed:28024296). Negatively regulates mTORC1 activation by inhibiting recruitment of mTORC1 to lysosomes upon stimulation with amino acids: acts by promoting the formation of a tightly bound supercomplex composed of the lysosomal V- ATPase, Ragulator and Rag GTPases, preventing recruitment of mTORC1 (PubMed:28024296). Acts as a regulator of muscle regeneration following injury by regulating mTORC1 activation (By similarity). .