May be involved in intracellular vesicle traffic. Inhibits ATF4-mediated transcription, possibly by dimerizing with ATF4 to form inactive dimers that cannot bind DNA. May be involved in regulating bone mass density through an ATF4-dependent pathway. May be involved in cell cycle progression. {ECO:0000269|PubMed:15911876, ECO:0000269|PubMed:18068885}. This is the function of TXLNG (taxilin gamma, ENSG00000086712).