Xeroderma pigmentosum (XP) is an autosomal recessive disease characterized by a high incidence of skin cancers. Yeast RAD30 encodes a DNA polymerase involved in the error-free bypass of ultraviolet (UV) damage. Here it is shown that XP variant (XP-V) cell lines harbor nonsense or frameshift mutations in hRAD30, the human counterpart of yeast RAD30. Of the eight mutations identified, seven would result in a severely truncated hRad30 protein. These results indicate that defects in hRAD30 cause XP-V, and they suggest that error-free replication of UV lesions by hRad30 plays an important role in minimizing the incidence of sunlight-induced skin cancers.

Activation of the mitogen-activated protein kinase (MAPK) cascade recently was discovered to play an important role in synaptic plasticity in area CA1 of rat hippocampus. However, the upstream mechanisms regulating MAPK activity and the downstream effectors of MAPK in the hippocampus are uncharacterized. In the present studies we observed that hippocampal MAPK activation is regulated by both the PKA and PKC systems; moreover, we found that a wide variety of neuromodulatory neurotransmitter receptors (metabotropic glutamate receptors, muscarinic acetylcholine receptors, dopamine receptors, and beta-adrenergic receptors) couple to MAPK activation via these two cascades. In additional studies we observed that PKC is a powerful regulator of CREB phosphorylation in area CA1. MAPK plays a critical role in transcriptional regulation by PKC, because MAPK activation is a necessary component for increased CREB phosphorylation in response to the activation of this kinase. Surprisingly, we also observed that MAPK activation is necessary for PKA coupling to CREB phosphorylation in area CA1. Overall, these studies indicate an unexpected richness of diversity in the regulation of MAPK in the hippocampus and suggest the possibility of a broad role for the MAPK cascade in regulating gene expression in long-term forms of hippocampal synaptic plasticity.

In both yeast and humans, DNA polymerase (Pol) eta functions in error-free replication of ultraviolet-damaged DNA, and Poleta promotes replication through many other DNA lesions as well. Here, we present evidence for the physical and functional interaction of yeast Poleta with proliferating cell nuclear antigen (PCNA) and show that the interaction with PCNA is essential for the in vivo function of Poleta. Poleta is highly inefficient at inserting a nucleotide opposite an abasic site, but interaction with PCNA greatly stimulates its ability for nucleotide incorporation opposite this lesion. Thus, in addition to having a pivotal role in the targeting of Poleta to the replication machinery stalled at DNA lesions, interaction with PCNA would promote the bypass of certain DNA lesions.

Y-family DNA polymerases, such as polymerase , polymerase , and polymerase , catalyze the bypass of DNA damage during translesion synthesis. These enzymes are recruited to sites of DNA damage by interacting with the essential replication accessory protein proliferating cell nuclear antigen (PCNA) and the scaffold protein Rev1. In most Y-family polymerases, these interactions are mediated by one or more conserved PCNA-interacting protein (PIP) motifs that bind in a hydrophobic pocket on the front side of PCNA as well as by conserved Rev1-interacting region (RIR) motifs that bind in a hydrophobic pocket on the C-terminal domain of Rev1. Yeast polymerase , a prototypical translesion synthesis polymerase, binds both PCNA and Rev1. It possesses a single PIP motif but not an RIR motif. Here we show that the PIP motif of yeast polymerase mediates its interactions both with PCNA and with Rev1. Moreover, the PIP motif of polymerase binds in the hydrophobic pocket on the Rev1 C-terminal domain. We also show that the RIR motif of human polymerase and the PIP motif of yeast Msh6 bind both PCNA and Rev1. Overall, these findings demonstrate that PIP motifs and RIR motifs have overlapping specificities and can interact with both PCNA and Rev1 in structurally similar ways. These findings also suggest that PIP motifs are a more versatile protein interaction motif than previously believed. Proliferating cell nuclear antigen (PCNA)2 is an essential protein that functions in DNA replication, repair, recombination, damage tolerance, and cell cycle control. It is a homotrimer that forms a ring-shaped clamp, which slides along DNA (1-3). Many proteins involved in DNA metabolism, the maintenance of genome stability, and cell cycle control possess PCNA-interacting protein (PIP) motifs that mediate their binding to PCNA (1, 4 -6). These PIP motifs contain two adjacent aromatic residues, which bind in a hydrophobic pocket on the front face of the PCNA ring (2, 4), and the binding of these PIP motifs to PCNA represents a major point of regulation for these proteins.Among the proteins that are regulated by PCNA are the Y-family DNA polymerases such as DNA polymerase (pol ), DNA polymerase (pol ), DNA polymerase (pol ), and Rev1 (7-12). These polymerases bypass DNA damage during translesion DNA synthesis in order to allow for continuous progression of the replication fork (13-16). Pol , for example, catalyzes the bypass of UV-induced thymine-thymine dimers and 8-oxoguanine lesions (17, 18). Defects in pol cause the variant form of xeroderma pigmentosum, a genetic disorder characterized by sensitivity to sunlight and a high incidence of skin cancers (19,20). Rev1, by contrast, bypasses damaged guanines and abasic sites (21-24).In addition to its catalytic function, Rev1 plays an important non-catalytic role in translesion synthesis by binding to other polymerases, like pol , pol , and pol , and acting as a scaffold to recruit them to PCNA (25-29). Many Y-family polymerases, such as mammalian pol , pol , and pol , possess short, conserved Rev1...

Rad30 is a member of the newly discovered UmuC/DinB/Rad30 family of DNA polymerases. The N-terminal regions of these proteins are highly homologous, and they contain five conserved motifs, I to V, while their C-terminal regions are quite divergent. We examined the contributions of the C-terminal and N-terminal regions of Rad30 to its activity and biological function. Although deletion of the last 54 amino acids has no effect on DNA polymerase or thymine-thymine (T-T) dimer bypass activity, this C-terminal deletion-containing protein is unable to perform its biological function in vivo. The presence of a bipartite nuclear targeting sequence within this region suggests that at least one function of this portion of Rad30 is nuclear targeting. To identify the active-site residues of Rad30 important for catalysis, we generated mutations of nine acidic residues that are invariant or highly conserved among Rad30 proteins from different eukaryotic species. Mutations of the Asp30 and Glu39 residues present in motif I and of the Asp155 residue present in motif III to alanine completely inactivated the DNA polymerase and T-T dimer bypass activities, and these mutations did not complement the UV sensitivity of the rad30⌬ mutation. Mutation of Glu156 in motif III to alanine confers a large reduction in the efficiency of nucleotide incorporation, whereas the remaining five Rad30 mutant proteins retain wild-type levels of DNA polymerase and T-T dimer bypass activities. From these observations, we suggest a role for the Asp30, Glu39, and Asp155 residues in the binding of two metal ions required for the reaction of the incoming deoxynucleoside 5-triphosphate with the 3-hydroxyl in the primer terminus, while Glu156 may participate in nucleotide binding.The RAD30 gene of Saccharomyces cerevisiae functions in error-free bypass of UV-induced DNA lesions (14, 23). RAD30 encodes a DNA polymerase, Pol, that has the ability to efficiently replicate through a cis-syn thymine-thymine (T-T) dimer, and it does so by inserting two A's opposite the two T's of the dimer (12). Inactivation of Pol in humans results in the cancer-prone syndrome, the variant form of xeroderma pigmentosum (11,22). Cells derived from individuals with the variant form of xeroderma pigmentosum exhibit a deficiency in the replication of UV-damaged DNA (2, 21), and they are hypermutable with UV light (30,33).Pol differs from other eukaryotic DNA polymerases in its ability to replicate proficiently through lesions which distort the DNA helix. For example, both the yeast and human Pol enzymes replicate through a cis-syn T-T dimer with the same efficiency and fidelity as they replicate through two undamaged T's (17, 31), and Pol efficiently bypasses an 8-oxoguanine lesion by predominantly inserting a C opposite the lesion (9). Since both of these lesions distort the template strand, the ability of Pol to bypass these and other distorting DNA lesions (8) must derive from an active site that is indifferent to geometric distortions in DNA. In keeping with this idea, Pol is a ...