Component of the small ribosomal subunit. The ribosome is a large ribonucleoprotein complex responsible for the synthesis of proteins in the cell (PubMed:23636399). Part of the small subunit (SSU) processome, first precursor of the small eukaryotic ribosomal subunit. During the assembly of the SSU processome in the nucleolus, many ribosome biogenesis factors, an RNA chaperone and ribosomal proteins associate with the nascent pre-rRNA and work in concert to generate RNA folding, modifications, rearrangements and cleavage as well as targeted degradation of pre-ribosomal RNA by the RNA exosome (PubMed:34516797). May play a role during erythropoiesis through regulation of transcription factor DDIT3 (By similarity). {ECO:0000255|HAMAP- Rule:MF_03122, ECO:0000269|PubMed:23636399, ECO:0000269|PubMed:34516797}. This is the function of RPS3A (ribosomal protein S3A, ENSG00000145425).