HSD5, or RNA, U1 small nuclear 4, is a human gene encoded by RNU1-4. It may also be known as: RNA, U1 small nuclear 4; HSD2; HSD6; HSD7; RNU1D2; RNU1E2; RNU1F1; RNU1G1; RNU1G2; U1B2; U1D2; U1E2; U1F. Homologs of this gene exist in other organisms, including: Arabidopsis.