The N-terminal fragment of ATF6-alpha contains a bZIP domain and binds the sequence CCACG in ER Stress Response Elements (ERSEs). ATF6-alpha binds ERSEs together with the heterotrimeric transcription factor NF-Y, which binds the sequence CCAAT in the ERSEs, and together the two factors activate transcription of ER stress-responsive genes. Evidence from overexpression and knockdowns indicates that ATF6-alpha is a potent activator but its homolog ATF6-beta is not and ATF6-beta may actually reduce expression of ER stress proteins. The XBP1 gene is transcribed to yield mRNA, the mRNA is spliced to yield Xbp(s) mRNA, and the mRNA is translated to yield protein.