AIDS drugs for Africa!' a case study examining transnational AIDS treatment activism and the reduction of global antiretroviral prices from 1996 to 2001

Includes abstract. Includes bibliographical references

Cell cycle-specific UNG2 phosphorylations regulate protein turnover, activity and association with RPA

Human UNG2 is a multifunctional glycosylase that removes uracil near replication forks and in non-replicating DNA, and is important for affinity maturation of antibodies in B cells. How these diverse functions are regulated remains obscure. Here, we report three new phosphoforms of the non-catalytic domain that confer distinct functional properties to UNG2. These are apparently generated by cyclin-dependent kinases through stepwise phosphorylation of S23, T60 and S64 in the cell cycle. Phosphorylation of S23 in late G1/early S confers increased association with replication protein A (RPA) and replicating chromatin and markedly increases the catalytic turnover of UNG2. Conversely, progressive phosphorylation of T60 and S64 throughout S phase mediates reduced binding to RPA and flag UNG2 for breakdown in G2 by forming a cyclin E/c-myc-like phosphodegron. The enhanced catalytic turnover of UNG2 p-S23 likely optimises the protein to excise uracil along with rapidly moving replication forks. Our findings may aid further studies of how UNG2 initiates mutagenic rather than repair processing of activation-induced deaminase-generated uracil at Ig loci in B cells

Uracil DNA N-Glycosylase Promotes Assembly of Human Centromere Protein A

Uracil is removed from DNA by the conserved enzyme Uracil DNA N-glycosylase (UNG). Previously, we observed that inhibiting UNG in Xenopus egg extracts blocked assembly of CENP-A, a histone H3 variant. CENP-A is an essential protein in all species, since it is required for chromosome segregation during mitosis. Thus, the implication of UNG in CENP-A assembly implies that UNG would also be essential, but UNG mutants lacking catalytic activity are viable in all species. In this paper, we present evidence that UNG2 colocalizes with CENP-A and H2AX phosphorylation at centromeres in normally cycling cells. Reduction of UNG2 in human cells blocks CENP-A assembly, and results in reduced cell proliferation, associated with increased frequencies of mitotic abnormalities and rapid cell death. Overexpression of UNG2 induces high levels of CENP-A assembly in human cells. Using a multiphoton laser approach, we demonstrate that UNG2 is rapidly recruited to sites of DNA damage. Taken together, our data are consistent with a model in which the N-terminus of UNG2 interacts with the active site of the enzyme and with chromatin

Novel dimeric structure of phage ϕ29-encoded protein p56: insights into uracil-DNA glycosylase inhibition

Protein p56 encoded by the Bacillus subtilis phage ϕ29 inhibits the host uracil-DNA glycosylase (UDG) activity. To get insights into the structural basis for this inhibition, the NMR solution structure of p56 has been determined. The inhibitor defines a novel dimeric fold, stabilized by a combination of polar and extensive hydrophobic interactions. Each polypeptide chain contains three stretches of anti-parallel β-sheets and a helical region linked by three short loops. In addition, microcalorimetry titration experiments showed that it forms a tight 2:1 complex with UDG, strongly suggesting that the dimer represents the functional form of the inhibitor. This was further confirmed by the functional analysis of p56 mutants unable to assemble into dimers. We have also shown that the highly anionic region of the inhibitor plays a significant role in the inhibition of UDG. Thus, based on these findings and taking into account previous results that revealed similarities between the association mode of p56 and the phage PBS-1/PBS-2-encoded inhibitor Ugi with UDG, we propose that protein p56 might inhibit the enzyme by mimicking its DNA substrate