Figure 2.

The basic leucine zipper (bZIP) transcription factor network of the amino acid response (AAR). The core of the transcription factor network that has been identified thus far to mediate the AAR consists of primarily bZIP family members. Several are transcriptionally activated by activating transcription factor (ATF) 4 [ATF3, CCAAT enhancer-binding protein homologous protein (CHOP), and CCAAT enhancer-binding protein (C/EBP) β] and then subsequently act to feedback inhibit the ATF4 signal as part of a self-limiting ATF4 program described in the text. C/EBPβ and cJUN are illustrated in the figure, but other members of the C/EBP and FOS/JUN families are known to be induced in expression by the AAR and/or contribute to regulation of AAR target genes. The solid arrows represent direct activation of the indicated gene, whereas the solid bars represent transcriptional antagonism of ATF4 action on AAR target genes. The dashed gray arrows indicate that ATF2 and cJUN stabilize the ATF4 protein by an unknown mechanism.