Clamping down on clamps and clamp loaders

Abstract

DNA transactions such as DNA replication and DNA repair require the concerted action of many enzymes, together with other proteins and non-protein cofactors. Among them three main accessory proteins, replication factor C (RF-C), proliferating-cell nuclear antigen (PCNA) and replication protein A (RP-A), are essential for accurate and processive DNA synthesis by DNA polymerases. RF-C is a complex consisting of five polypeptides with distinct functions. RF-C can bind to a template-primer junction and, in the presence of ATP, load the PCNA clamp onto DNA, thereby recruiting DNA polymerases to the site of DNA synthesis. RF-C not only acts as a clamp loader in DNA replication and DNA repair, but there is some evidence that it could be involved in several other processes such as transcription, S-phase checkpoint regulation, apoptosis, differentiation and telomere-length regulation.Keywords : eukaryotic DNA replication; replication factor C; proliferating-cell nuclear antigen; clamp; clamp loader ; DNA polymerase δ ; S-phase checkpoint regulation ; apoptosis; differentiation; telomere. Of clamps and clamp loadersrespective clamps onto DNA. High sequence similarity between the clamp loaders suggest that their mechanisms of action may DNA replication, one of the most remarkable and challeng-be very similar [4]. The eukaryotic RF-C clamp loader consists ing cellular events, is the result of the collaboration of a formida-of five distinct subunits (Table 1), as does the E. coli γ complex. ble amount of proteins. The mechanisms at the basis of this By loading the homotrimer proliferating-cell nuclear antigen complicated event are similar in prokaryotes and eukaryotes, de-(PCNA) clamp onto DNA, it confers high processivity to polyspite the evolutionary distance. In each of these cell types, the merases δ and ε. Despite there being virtually no similarity in replicative polymerases are chaperoned by several accessory sequence between β and PCNA, the three-dimensional structures proteins that confer speed and high processivity.are almost identical [5]. The amino acid sequence of PCNA is Responsible for DNA replication in Escherichia coli is the only approximately 70% the length of that of β, so that three DNA polymerase III holoenzyme, a ten-subunit complex (Ta-monomers of PCNA are required to form the typical doughnutble 1) [1]. The DNA polymerase (polymerase III core) consists like structure, in contrast to β where only two monomers are of A (the polymerase), ε (the proofreading exonuclease) and θ enough. The T4 gene 44/62 protein complex contains five subsubunits. The clamp loader, called γ complex, contains five subunits, four protomers of the gene 44 protein and one copy of the units, γ, δ, δ′, ψ and χ, and is required for the ATP-dependent gene 62 protein [6]. It is required for the loading of the product assembly of the β clamp onto DNA. Contrary to all eukaryotes of gene 45, the T4 bacteriophage counterpart of PCNA and E. and the T4 phage, E. coli contains an additional connector procoli β. Despite the apparent similar...

Proteome analysis of nuclear matrix proteins during apoptotic chromatin condensation

“…40,50 Interestingly, these proteins were found accumulated in the nuclear matrix fraction not only during apoptosis, but also in normal HeLa cells during G1/S transition (C Gerner and W Mikulits, unpublished data). This observation may suggest the induction of replicative foci and of DNA repair during apoptosis as described by others.…”

The malarial CDK Pfmrk and its effector PfMAT1 phosphorylate DNA replication proteins and co-localize in the nucleus

“…RFC loads the "sliding clamp" PCNA (proliferating cell nuclear antigen) onto DNA during replication. The loading of PCNA onto DNA by RFC is an important step in DNA replication and increases the processivity of DNA polymerase [32]. The RFC subunits share eight regions of high sequence similarity that include regions involved in protein complex formation, DNA binding, PCNA binding and DNA replication [32].…”

“…The loading of PCNA onto DNA by RFC is an important step in DNA replication and increases the processivity of DNA polymerase [32]. The RFC subunits share eight regions of high sequence similarity that include regions involved in protein complex formation, DNA binding, PCNA binding and DNA replication [32]. The motifs identified in PfRFC-5 when queried on the NCBI Entrez website (http://www.ncbi.nlm.nih.gov/Structure/cdd/cddsrv.cgi) include (i) an ATP-binding site encompassing residues 41-48 and residues 132 and 161, (ii) the WalkerA motif {consensus sequence GxxGxGK(S/T)} encompassing residues 40-47, (iii) the WalkerB motif consensus {contains four aliphatic residues followed by two negatively-charged residues}, encompassing residues 128-133 and (iv) an Arginine finger, residue 175 (Fig.…”

MyD genes in negative growth control

“…Evidence has accumulated that MyD/Gadd proteins display a complex array of physical interactions, including homologous and heterologous interactions with each other, as well as with products of cell cycle regulatory genes. It was found that MyD118 and Gadd45 associate with PCNA Hall et al, 1995;Vairapandi et al, 1996), which plays a central role in DNA repair and DNA replication (Mossi and Hubscher 1998;Prosperi, 1997;Jonsson and Hubscher, 1997). MyD118 and Gadd45 were shown also to associate with the cyclin dependent kinase inhibitor p21 (Vairapandi et al, 1996), known to interact with PCNA and to inhibit DNA replication Li et al, 1994;Flores-Rozas et al, 1994).…”