Proteins in this family are phosphodiesterases responsible for trimming the poly (U) tract of the last nucleotides in the pre-U6 snRNA molecule, leading to the formation of mature U6 snRNA [, ].In Saccharomyces cerevisiae, Usb1 is an essential protein that localises to the nucleus and mitochondria []. Usb1 overexpression can compensate for specific respiratory defects of an oxa1 yeast mutant []. In humans, Usb1 is localised to the nucleus and is involved in the 2',3'-cyclic phosphate formation at the 3' end of U6 snRNA []. The human protein has been shown to degrade both oligo(U) and oligo(A) tails at the 3' end of U6 snRNA []. Its crystal structure has been solved and shows a globular α-β-type architecture []. Mutation in Usb1 is linked to poikiloderma with neutropenia (PN), a genodermatosis characterised by poikiloderma, pachyonychia and chronic neutropenia [, ].
