Component of the spliceosomal U1 snRNP, which is essential for recognition of the pre-mRNA 5' splice-site and the subsequent assembly of the spliceosome (PubMed:19325628, PubMed:25555158). SNRNP70 binds to the loop I region of U1-snRNA (PubMed:19325628, PubMed:2467746, PubMed:25555158). {ECO:0000269|PubMed:19325628, ECO:0000269|PubMed:2467746, ECO:0000269|PubMed:25555158}. [Isoform 3]: Truncated isoforms that lack the RRM domain cannot bind U1-snRNA. . [Isoform 4]: Truncated isoforms that lack the RRM domain cannot bind U1-snRNA. . This is the function of Ensembl gene identifier ENSG00000104852 (SNRNP70, small nuclear ribonucleoprotein U1 subunit 70).