May play a role during erythropoiesis through regulation of transcription factor DDIT3. Component of the small ribosomal subunit. Mature ribosomes consist of a small (40S) and a large (60S) subunit. The 40S subunit contains about 33 different proteins and 1 molecule of RNA (18S). The 60S subunit contains about 49 different proteins and 3 molecules of RNA (28S, 5.8S and 5S). Identified in a IGF2BP1-dependent mRNP granule complex containing untranslated mRNAs. Binds with high affinity to IPO4. Interacts with DDIT3. Localized in cytoplasmic mRNP granules containing untranslated mRNAs. ADP-ribosylated at Tyr-155 by PARP1 in presence of HPF1. Belongs to the eukaryotic ribosomal protein eS1 family.