The function of USB1 (U6 snRNA biogenesis phosphodiesterase 1, ENSG00000103005) is as follows. 3'-5' RNA exonuclease that trims the 3' end of oligo(U) and oligo(A) tracts of the pre-U6 small nuclear RNA (snRNA) molecule, leading to the formation of a mature U6 snRNA 3' end-terminated with a 2',3'-cyclic phosphate (PubMed:22899009, PubMed:23022480, PubMed:23190533, PubMed:26213367, PubMed:28887445, PubMed:30215753, PubMed:31832688). Participates in the U6 snRNA 3' end processing that prevents U6 snRNA degradation (PubMed:22899009, PubMed:23022480, PubMed:23190533, PubMed:26213367, PubMed:28887445, PubMed:30215753, PubMed:31832688). In addition also removes uridines from the 3' end of U6atac snRNA and possibly the vault RNA VTRNA1-1 (PubMed:26213367). {ECO:0000269|PubMed:22899009, ECO:0000269|PubMed:23022480, ECO:0000269|PubMed:23190533, ECO:0000269|PubMed:26213367, ECO:0000269|PubMed:28887445, ECO:0000269|PubMed:30215753, ECO:0000269|PubMed:31832688}.