MicroProteins: Expanding functions and novel modes of regulation
Résumé
MicroProteins are small, 5–15-kDa single-domain proteins that are evolutionarily related to multi-domain proteins with sequence homology (Eguen et al., 2015). The single domain of microProteins is often a protein–protein interaction (PPI) domain, through which they can interact with their multi-domain protein targets (Figure 1). The first experimental insight that microProteins exist and how they act came from the identification of the regulatory feedback mechanism of class III homeodomain-leucine zipper (HD-ZIPIII) transcription factors by LITTLE ZIPPER (ZPR) microProteins (Wenkel et al., 2007; Kim et al., 2008). In Arabidopsis, the LITTLE ZIPPER microProtein family consists of four members (ZPR1-4) containing only a leucine zipper domain. The HD-ZIPIII transcription factor REVOLUTA directly transcriptionally upregulates multiple ZPR genes. ZPR proteins physically interact with their HD-ZIPIII targets and suppress their DNA binding ability. Thus, ZPRs establish a direct negative feedback module that controls the activity of the shoot apical meristem.