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). ; [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.