In 1990, three groups simultaneously demonstrated that a gene located on the class II region regulates the class I antigen presentation (Deverson et al., Nature 348:738, 1990; Trowsdale et al., Nature 348:741, 1990; Spies et al., Nature 348:744, 1990). The gene codes for an ATP-binding cassette (ABC) superfamily of transporter proteins that transport peptides from the cytoplasm into the ER, where peptides are loaded into nascent class I molecules. The protein was named TAP.