InterPro domain: IPR027521

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 [ 1 ].

In Saccharomyces cerevisiae, Usb1 is an essential protein that localises to the nucleus and mitochondria [ 2 ]. Usb1 overexpression can compensate for specific respiratory defects of an oxa1 yeast mutant [ 3 ].

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 [ 4 ]. The human protein has been shown to degrade both oligo(U) and oligo(A) tails at the 3' end of U6 snRNA [ 4 ]. Its crystal structure has been solved and shows a globular alpha-beta-type architecture [ 5 ]. Mutation in Usb1 is linked to poikiloderma with neutropenia (PN), a genodermatosis characterised by poikiloderma, pachyonychia and chronic neutropenia [ 5 , 6 ].

1. C16orf57, a gene mutated in poikiloderma with neutropenia, encodes a putative phosphodiesterase responsible for the U6 snRNA 3' end modification. Genes Dev. 26, 1911-25
2. Global analysis of protein localization in budding yeast. Nature 425, 686-91
3. An in silico approach combined with in vivo experiments enables the identification of a new protein whose overexpression can compensate for specific respiratory defects in Saccharomyces cerevisiae. BMC Syst Biol 5, 173
4. Aberrant 3' oligoadenylation of spliceosomal U6 small nuclear RNA in poikiloderma with neutropenia. Blood 121, 1028-38
5. Targeted next-generation sequencing appoints c16orf57 as clericuzio-type poikiloderma with neutropenia gene. Am. J. Hum. Genet. 86, 72-6
6. Identification of a homozygous deletion mutation in C16orf57 in a family with Clericuzio-type poikiloderma with neutropenia. Am. J. Med. Genet. A 152A, 1347-8