ATP insertion opposite 8-oxo-deoxyguanosine by Pol4 mediates error-free tolerance in Schizosaccharomyces pombe.

7,8-Dihydro-8-oxo-deoxyguanosine (8oxodG) is a highly premutagenic DNA lesion due to its ability to mispair with adenine. Schizosaccharomyces pombe lacks homologs for relevant enzymes that repair 8oxodG, which suggests that this lesion could be persistent and must be tolerated. Here we show that SpPol4, the unique PolX in fission yeast, incorporates ATP opposite 8oxodG almost exclusively when all nucleotides (ribos and deoxys) are provided at physiological concentrations.

A specific N-terminal extension of the 8 kDa domain is required for DNA end-bridging by human Polμ and Polλ.

Human DNA polymerases mu (Polµ) and lambda (Polλ) are X family members involved in the repair of double-strand breaks in DNA during non-homologous end joining. Crucial abilities of these enzymes include bridging of the two 3' single-stranded overhangs and trans-polymerization using one 3' end as primer and the other as template, to minimize sequence loss. In this context, we have studied the importance of a previously uncharacterised sequence ('brooch'), located at the N-terminal boundary of the Polß-like polymerase core, and formed by Tyr(141), Ala(142), Cys(143), Gln(144) and Arg(145) in Polµ, and by Trp(239), Val(240), Cys(241), Ala(242) and Gln(243) in Polλ.

The BRCT domain and the specific loop 1 of human Polμ are targets of Cdk2/cyclin A phosphorylation.

Human family X polymerases contribute both to genomic stability and variability through their specialized functions in DNA repair. Polμ participates in the repair of spontaneous double strand breaks (DSB) by non homologous end-joining (NHEJ), and also in the V(D)J recombination process after programmed DSBs. Polμ plays this dual role due to its template-dependent and terminal transferase (template-independent) polymerization activities.

Ribonucleotides and manganese ions improve non-homologous end joining by human Polμ.

Human DNA polymerase mu (Polμ), a family X member involved in DNA repair, has both template-directed and terminal transferase (template-independent) activities. In addition to their ability to incorporate untemplated nucleotides, another similarity between Polµ and terminal deoxynucleotidyl transferase (TdT) is their promiscuity in using ribonucleotides (NTPs), whose physiological significance is presently unknown. As shown here, Polµ can use NTPs instead of deoxynucleotides (dNTPs) during non-homologous end joining (NHEJ) of non-complementary ends, a Polµ-specific task.

The Flp1/Clp1 phosphatase cooperates with HECT-type Pub1/2 protein-ubiquitin ligases in Schizosaccharomyces pombe.

The Schizosaccharomyces pombe Flp1p serine-threonine phosphatase is required for the degradation of the mitotic inducer Cdc25p at the end of mitosis. Cdc25p degradation prevents Cdc2p-tyrosine 15 dephosphorylation and, thus, contributes to the timely inactivation of mitotic CDK-associated kinase activity. Both RING- and HECT-type protein-ubiquitin ligases are involved in Cdc25p destabilization.

Human Cdc14A reverses CDK1 phosphorylation of Cdc25A on serines 115 and 320.

Human Cdc14A is an evolutionary conserved dual-specificity protein phosphatase that reverses the modifications effected by cyclin-dependent kinases and plays an important role in centrosome duplication and mitotic regulation. Few substrates of Cdc14A have been identified, some of them with homologues in yeast that, in turn, are substrates of the Saccharomyces cerevisiae Cdc14 homologue, a protein phosphatase essential for yeast cell viability owing its role in mitotic exit regulation. Identification of the physiological substrates of human Cdc14A is an immediate goal in order to elucidate which cellular processes it regulates.

Functional homology among human and fission yeast Cdc14 phosphatases.

Budding and fission yeast Cdc14 homologues, a conserved family of serine-threonine phosphatases, play a role in the inactivation of mitotic cyclin-dependent kinases (CDKs) by molecularly distinct mechanisms. Saccharomyces cerevisiae Cdc14 protein phosphatase inactivates CDKs by promoting mitotic cyclin degradation and the accumulation of a CDK inhibitor to allow budding yeast cells to exit from mitosis. Schizosaccharomyces pombe Flp1 phosphatase down-regulates CDK/cyclin activity, controlling the degradation of the Cdc25 tyrosine phosphatase for fission yeast cells to undergo cytokinesis.

A role for the Cdc14-family phosphatase Flp1p at the end of the cell cycle in controlling the rapid degradation of the mitotic inducer Cdc25p in fission yeast.

The Schizosaccaromyces pombe protein Flp1p belongs to a conserved family of serine-threonine-phosphatases. The founding member of this family, Saccharomyces cerevisiae Cdc14p, is required for inactivation of mitotic CDKs and reversal of CDK mediated phosphorylation at the end of mitosis, thereby bringing about the M-G1 transition. Initial studies of Flp1p suggest that it may play a different role to Cdc14p.