C16orf57 encodes a human protein of unknown function, and mutations in the gene occur in poikiloderma with neutropenia (PN), which is a rare, autosomal recessive disease. Interestingly, mutations in C16orf57 were also observed among patients diagnosed with Rothmund-Thomson syndrome (RTS) and dyskeratosis congenita (DC), which are caused by mutations in genes involved in DNA repair and telomere maintenance. A genetic screen in Saccharomyces cerevisiae revealed that the yeast ortholog of C16orf57, USB1 (YLR132C), is essential for U6 small nuclear RNA (snRNA) biogenesis and cell viability. Usb1 depletion destabilized U6 snRNA, leading to splicing defects and cell growth defects, which was suppressed by the presence of multiple copies of the U6 snRNA gene SNR6. Moreover, Usb1 is essential for the generation of a unique feature of U6 snRNA; namely, the 39-terminal phosphate. RNAi experiments in human cells followed by biochemical and functional analyses confirmed that, similar to yeast, C16orf57 encodes a protein involved in the 29,39-cyclic phosphate formation at the 39 end of U6 snRNA. Advanced bioinformatics predicted that C16orf57 encodes a phosphodiesterase whose putative catalytic activity is essential for its function in vivo. Our results predict an unexpected molecular basis for PN, DC, and RTS and provide insight into U6 snRNA 39 end formation.

REPAIRtoire is the first comprehensive database resource for systems biology of DNA damage and repair. The database collects and organizes the following types of information: (i) DNA damage linked to environmental mutagenic and cytotoxic agents, (ii) pathways comprising individual processes and enzymatic reactions involved in the removal of damage, (iii) proteins participating in DNA repair and (iv) diseases correlated with mutations in genes encoding DNA repair proteins. REPAIRtoire provides also links to publications and external databases. REPAIRtoire contains information about eight main DNA damage checkpoint, repair and tolerance pathways: DNA damage signaling, direct reversal repair, base excision repair, nucleotide excision repair, mismatch repair, homologous recombination repair, nonhomologous end-joining and translesion synthesis. The pathway/protein dataset is currently limited to three model organisms: Escherichia coli, Saccharomyces cerevisiae and Homo sapiens. The DNA repair and tolerance pathways are represented as graphs and in tabular form with descriptions of each repair step and corresponding proteins, and individual entries are cross-referenced to supporting literature and primary databases. REPAIRtoire can be queried by the name of pathway, protein, enzymatic complex, damage and disease. In addition, a tool for drawing custom DNA–protein complexes is available online. REPAIRtoire is freely available and can be accessed at http://repairtoire.genesilico.pl/.

Base excision repair (BER) pathway executed by a complex network of proteins is the major system responsible for the removal of damaged DNA bases and repair of DNA single strand breaks (SSBs) generated by environmental agents, such as certain cancer therapies, or arising spontaneously during cellular metabolism. Both modified DNA bases and SSBs with ends other than 3'-OH and 5'-P are repaired either by replacement of a single or of more nucleotides in the processes called short-patch BER (SP-BER) or long-patch BER (LP-BER), respectively. In contrast to Escherichia coli cells, in human ones, the two BER sub-pathways are operated by different sets of proteins. In this review the selection between SP- and LP-BER and mutations in BER and end-processors genes and their contribution to bacterial mutagenesis and human diseases are considered.