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 (25S, 5.8S and 5S). There are two genes for S1 in S.pombe. Belongs to the eukaryotic ribosomal protein eS1 family.