Unusual insertion element polymorphisms in the promoter and terminator regions of the mucAB-like genes of R471a and R446b

We have previously identified umu-complementing genes on two incL/M plasmids, R471a and R446b (C. Ho et al., J. Bacteriol., 175 (1993) 5411-5419). Molecular analysis of these genes revealed that they are more structurally and functionally related to mucAB from the incN plasmid pKM101 than to other members of the previously identified Umu-like family. As a consequence, we have termed these new homologs mucAB(R471a) and mucAB(R446b) respectively. Interestingly, while the location of the mucAB-like genes is essentially the same in both R471a and R446b, the regions immediately flanking the mucAB-like genes are highly polymorphic. For example, 5' to mucAB(R471a) we found an insert that appears to be a novel retroelement encoding a putative reverse transcriptase (RT). This RT is related to the reverse transcriptases encoded by group II introns but is embedded in a retron-like context. Immediately 3' to the mucAB(R471a) locus is a putative insertion element of a sparsely-dispersed class not previously reported from enteric bacteria. Both the RT and insertion element are absent in R446b. These observations suggest that the mucAB-like genes from R471a and R446b are located within regions of the R-plasmids that perhaps were once (or still are) mobile genetic elements. Such observations might help explain the distribution of umu-like genes on R-plasmids and bacterial chromosomes.

Intrahypothalamic discriminative stimulus effects of neuropeptide Y

Neuropeptide Y (NPY) is one of the most ubiquitous neurotransmitters in the CNS and has been implicated in a variety of psychological and physiological functions. The current study investigated whether intrahypothalamic (I.H.) administrations of NPY were behaviorally discriminable from saline injections. Rats were trained to differentially respond based on whether they received I.H. injections of NPY (0.5 microg/0.5 microl) or saline (0.5 microl 0.9% NaCl). Subjects demonstrated discriminative control (85% correct in 8 out of 10 consecutive sessions) after a mean of 32 sessions. The ability of subjects to discriminate I.H. NPY from saline was dose dependent, with the lowest NPY dose tested (0.03 microg/0.5 microl) generalizing to saline. The opioid antagonist naloxone blocked the discrimination of NPY when administered I.P. (3.0 mg/kg) or I.H. (50 microg/0.5 microl).

Effects of the opioid antagonist naltrexone on feeding induced by DAMGO in the central nucleus of the amygdala and in the paraventricular nucleus in the rat

The paraventricular nucleus of the hypothalamus (PVN) and the central nucleus of the amygdala (CNA) are two forebrain structures which are important in regulation of ingestive behavior. DAMGO is one of the most reliable and potent mu-selective opioid ligands that increases feeding in both of these brain nuclei. Administration of naloxone, an opioid antagonist, into the CNA prior to DAMGO blocks DAMGO-induced increases in food intake. The effect of this drug combination on food intake has not been evaluated in the PVN. However, intra-PVN injection of naloxone decreases deprivation and NPY-induced feeding. It has been suggested that CNA may modulate activity of midbrain and caudal brainstem centers via the hypothalamus. Based on these data, we evaluated whether an opioid-opioid interaction is present between the CNA and PVN which might affect feeding behavior. To test this, rats were doubly cannulated with 1 cannula placed in the PVN and 1 cannula in the CNA, allowing for co-administration of the opioid agonist into the PVN and the opioid antagonist into the CNA, and vice versa. CNA DAMGO increased feeding more than two-fold as compared to the vehicle-injected rats. When doses of 10, 12.5 and 25 micrograms of naltrexone (NTX) were injected into the PVN, CNA DAMGO no longer increased food intake above control levels. In the reverse situation, PVN DAMGO also increased food intake above control levels. However, when NTX was administrated unilaterally into the CNA at a relatively high dose (25 micrograms) or bilaterally (12.5 micrograms), PVN DAMGO-induced feeding was not altered. This suggests that an opioid-opioid signaling pathway exists from the CNA to the PVN which influences feeding via mu opioid receptors, whereas such a pathway from the PVN to the CNA does not seem to exist.

Transforming patient feedback into strategic action plans

Patients' perceptions provide valuable insight into areas for improvement and opportunities for strategic planning. Using both quantitative and qualitative research methods, the topics of what drives patient satisfaction, what delights patients, and what disappoints patients were examined. A case study approach was used to develop strategic recommendations for two market segments. For primary care patients, recommendations revolve around "provider caring" and "choice." For specialty patients, recommendations concentrate on "provider caring," "provider competence," and "office wait time."

The Saccharomyces cerevisiae RAD30 gene, a homologue of Escherichia coli dinB and umuC, is DNA damage inducible and functions in a novel error-free postreplication repair mechanism

Damage-inducible mutagenesis in prokaryotes is largely dependent upon the activity of the UmuD'C-like proteins. Since many DNA repair processes are structurally and/or functionally conserved between prokaryotes and eukaryotes, we investigated the role of RAD30, a previously uncharacterized Saccharomyces cerevisiae DNA repair gene related to the Escherichia coli dinB, umuC and S. cerevisiae REV1 genes, in UV resistance and UV-induced mutagenesis. Similar to its prokaryotic homologues, RAD30 was found to be damage inducible. Like many S. cerevisiae genes involved in error-prone DNA repair, epistasis analysis clearly places RAD30 in the RAD6 group and rad30 mutants display moderate UV sensitivity reminiscent of rev mutants. However, unlike rev mutants, no defect in UV-induced reversion was seen in rad30 strains. While rad6 and rad18 are both epistatic to rad30, no epistasis was observed with rev1, rev3, rev7 or rad5, all of which are members of the RAD6 epistasis group. These findings suggest that RD30 participates in a novel error-free repair pathway dependent on RAD6 and RAD18, but independent of REV1, REV3, REV7 and RAD5.

Role of carbohydrate type on diet selection in neuropeptide Y-stimulated rats

We tested whether carbohydrate source (corn starch, sucrose, Polycose) influences the choice between a high-fat and high-carbohydrate diet in spontaneously feeding rats and in rats stimulated to eat by neuropeptide Y (NPY) administration or food deprivation. Rats were tested under three diet options: 1) a high-fat diet versus a high-corn starch diet; 2) a high-fat diet versus a high-sucrose diet, and 3) a high-fat diet versus a high-Polycose diet. During daily and stimulated feeding rats ate more of the high-carbohydrate diet than the fat diet when the source of carbohydrate was sucrose or Polycose; however, when corn starch was provided as the carbohydrate source rats ate more of the high-fat diet. Food-deprived rats increased intake of both the high-fat and the high-carbohydrate diets, with the proportion of energy ingested from each of the diets resembling that noted during 3 days of spontaneous feeding. NPY-injected rats ate more of both the high-fat and high-carbohydrate diets during diet options 1 and 3, but not during option 2 when the high-sucrose and high-fat diets were offered concurrently. In that case, rats did not significantly increase their intake of the high-fat diet. Although carbohydrate source and NPY administration each influenced diet selection, altering the source of carbohydrate had a more marked effect.

A sucrose-based maintenance diet increases sensitivity to appetite suppressant effects of naloxone

Rats maintained under restricted access to food (but at 100% free-feeding weights) received one of two diets in their home cages: a palatable sucrose-based diet, or regular chow (grain based diet), and could respond for either sucrose- or grain-based reinforcers under an FR 40 reinforcement schedule (crossover design). Naloxone (0, 0.1, 0.3, 1.0, and 3.0 mg/kg) was more potent in reducing operant-chamber responding in rats maintained on a sucrose-based diet in their home cages than those fed a grain-based diet, regardless of the type of pellets available in the operant chambers. Whereas naloxone decreased response rate over the session, it had no effect on initiation of responding. Results support the hypothesis that opioids are involved in the maintenance, but not the initiation of consummatory behavior. Furthermore, increased potency of naloxone following chronic ingestion of palatable food is similar to that observed following chronic opiate administration, suggesting a relationship between palatability and opioids.

Lactation decreases mRNA levels of opioid peptides in the arcuate nucleus of the rat

The state of lactation results in increased food intake to compensate for the increased energy expenditure to produce nutrients supplied to the offspring. In this study, Sprague-Dawley female rats lactating for 10-16 days, and rats 7 days post-lactation were implanted with osmotic minipumps infusing either naltrexone (NTX) (70 microg/h) or saline (0.9%) over a 48 h period. mRNA levels of pro-dynorphin (proDYN), pro-opiomelanocortin (POMC) and pro-enkephalin (proENK) were measured in the arcuate nucleus (ARC) and whole pituitary of both groups. In both saline- and NTX-treated lactating subjects, food intake was higher than in post-lactating subjects (P < 0.01). In post-lactating subjects, NTX decreased food intake by 27% during the infusion period (P < 0.05). There were no significant differences in body weight between the treatment groups; however, naltrexone decreased body weight gain in both lactating and post-lactating subjects. In both saline and NTX-treated lactating subjects, ARC mRNA levels of proDYN, POMC and proENK were significantly decreased compared with the saline or NTX-treated post-lactating subjects (P < 0.01). NTX did not significantly influence gene expression of opioid peptides in the ARC in either the lactating or the post-lactating subjects. Neither the lactation condition nor NTX administration significantly changed mRNA levels of proDYN, POMC or proENK in whole pituitary. Thus, as has been noted in energy-deprived rats, opioid peptide gene expression is decreased in the ARC of lactating rats, a period during which rats have increased energy requirements.

Evidence for the presence of the platelet-activating factor receptor in the CFW mouse preimplantation two-cell-stage embryo

Platelet-activating factor (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine; PAF), a potent signaling phospholipid, has a significant role in preimplantation embryo development. CFW mouse embryos respond to PAF with improved development and implantation rates. PAF's signal transduction mechanism in other cell types is receptor mediated. However, embryonic mRNA for the PAF receptor has not been detected. The study objectives were to determine the presence of PAF receptor mRNA in CFW mouse two-cell embryos by reverse transcription (RT)-polymerase chain reaction and Northern blot analysis and to ascertain the effect of PAF on intracellular calcium levels (a receptor-mediated event). Total RNA was purified by acid-phenol extraction and ethanol precipitation. Complementary DNA was synthesized by RT. RNA was primed with oligo-dT plus PAF receptor-specific primer (3' to 5') at 42 degrees C for 60 min, 95 degrees C for 10 min, and 5 degrees C for 5 min. The RT product was amplified with Taq polymerase and PAF receptor-specific primer (5' to 3') at 94 degrees C for 5 min and 54 degrees C for 5 min for one cycle, and at 72 degrees C for 3 min, 93 degrees C for 90 sec, and 61 degrees C for 150 sec for 30 cycles followed by 72 degrees C for 10 min and then holding at 4 degrees C. The product was analyzed by agarose gel electrophoresis, producing a single band (610 base pairs [bp]), thus demonstrating the presence of PAF-receptor mRNA. Sequence analysis of the cloned 610-bp fragment confirmed that it is the PAF receptor. Northern blot analysis also confirmed the expression of the PAF receptor in the CFW mouse preimplantation two-cell-stage embryo. PAF treatment of the two-cell-stage CFW mouse embryo resulted in a fourfold increase in intracellular calcium over background levels.

Simian virus-40 large-T antigen binds p53 in human mesotheliomas

We found that simian virus 40 (SV40) induces mesotheliomas in hamsters and that 60% of human mesotheliomas contain and express SV40 sequences, results now confirmed by others [ref. 3-5, and presentations by D. Griffiths & R. Weiss, F. Galateau-SallE, and H.I.P. at "Simian virus 40: A possible human polyoma virus," NIH workshop, 27-28 January 1997, Bethesda, MD (transcript available through SAG Corp., Washington, DC 20008)]. Mesothelioma, an aggressive malignancy resistant to therapy, originates from the serosal lining of the pleural, pericardial and peritoneal cavities. The incidence of mesothelioma continues to increase worldwide because of exposure to crocidolite asbestos. However, at least 20% of mesotheliomas in the United States are not associated with asbestos exposure, and only a minority of people exposed to high concentrations of asbestos develop mesothelioma. Thus, other carcinogens may induce mesothelioma in individuals not exposed to asbestos, and/or may render particular individuals more susceptible to the carcinogenic effect of asbestos. We investigated whether the expression of the SV40 large T-antigen (Tag) interferes with the normal expression of the tumor suppressor gene p53 in human mesotheliomas. We found that SV40 Tag retains its ability to bind and to inactivate p53, a cellular protein that when normally expressed plays an important role in suppressing tumor growth and in inducing sensitivity to therapy. Our findings do not establish a cause-and-effect relation, but indicate that the possibility that SV40 contributes to the development of human mesotheliomas should be carefully investigated.

Interaction of the hypothalamic paraventricular nucleus and central nucleus of the amygdala in naloxone blockade of neuropeptide Y-induced feeding revealed by c-fos expression

Neuropeptide Y (NPY) is a powerful inducer of food intake with a key site of action in the paraventricular nucleus (PVN) of the hypothalamus. An effective method for inhibiting the effects of NPY is pretreatment with the opioid antagonists naloxone or naltrexone. In the present study, we used immunohistochemistry for cFos as a marker of neuronal activity to map the effects of PVN-injected NPY and blockade of these effects by peripheral injection of naloxone. Injection of NPY into the PVN resulted in an increase in food intake that was blocked by peripheral administration of naloxone. PVN NPY also resulted in increased cFos immunoreactivity (cFos-IR) in the PVN independent of food intake, and although peripheral naloxone inhibited NPY-induced feeding, it did not alter cFos-IR in the PVN. cFos-IR in the central nucleus of the amygdala (CNA) increased in response to both NPY and naloxone. Furthermore, the response to NPY and naloxone was additive, suggesting that peripheral naloxone and PVN NPY activate different neuronal populations in the CNA. Three other brain regions, the nucleus of the solitary tract, the ventrolateral medulla, and the supraoptic nucleus, all showed increases in cFos-IR in this study, but these changes came only as a result of increased food intake after PVN-injected NPY. The current data suggest that the CNA is a site important for the integration of the NPY and opioid systems.

Recruitment of p300/CBP in p53-dependent signal pathways

The products of the p53 and CBP/p300 genes have been individually implicated in control of cell growth and regulation of transcription. p53 is known to act as a positive and negative regulator of gene expression. Here we show that p53, in both wild-type and mutant conformation, forms a specific protein complex with p300. However, in its wild-type but not mutant conformation, p53 inhibits a promoter containing the DNA-binding sequences for the transcription factor AP1, in a p300-dependent manner. p300 stimulates the transcriptional activity of p53 on p53-regulated promoters, and it enhances the responsiveness to a physiological upstream modulator of p53 function, ionizing radiation. A dominant negative form of p300 prevents transcriptional activation by p53, and it counteracts p53-mediated G1 arrest and apoptosis. The data implicate p300 as an important component of p53-signaling, thus providing new insight into the mechanisms of cellular proliferation.

Translocation of a UV-damaged DNA binding protein into a tight association with chromatin after treatment of mammalian cells with UV light

A UV-damaged DNA binding protein (UV-DDB) is the major source of UV-damaged DNA binding activity in mammalian cell extracts. This activity is defective in at least some xeroderma pigmentosum group E (XP-E) patients; microinjection of the UV-DDB protein into their fibroblasts corrects nucleotide excision repair (NER). In an in vitro reconstituted NER system, small amounts of UV-DDB stimulate repair synthesis a few fold. After exposure to UV, mammalian cells show an early dose-dependent inhibition of the extractable UV-DDB activity; this inhibition may reflect a tight association of the binding protein with UV-damaged genomic DNA. To investigate the dynamics and location of UV-DDB with respect to damaged chromatin in vivo, we utilized nuclear fractionation and specific antibodies and detected translocation of the p127 component of UV-DDB from a loose to a tight association with chromatinized DNA immediately after UV treatment. A similar redistribution was found for other NER proteins, i.e. XPA, RP-A and PCNA, suggesting their tighter association with genomic DNA after UV. These studies revealed a specific protein-protein interaction between UV-DDB/p127 and RP-A that appears to enhance binding of both proteins to UV-damaged DNA in vitro, providing evidence for the involvement of UV-DDB in the damage-recognition step of NER. Moreover, the kinetics of the reappearance of extractable UV-DDB activity after UV treatment of human cells with differing repair capacities positively correlate with the cell's capacity to repair 6–4 pyrimidine dimers (6–4 PD) in the whole genome, a result consistent with an in vivo role for UV-DDB in recognizing this type of UV lesion.

Effect of naltrexone on feeding, neuropeptide Y and uncoupling protein gene expression during lactation

Neuropeptide Y increases feeding and decreases measures of brown adipose tissue thermogenesis. In lactating rats, increased feeding, increased hypothalamic neuropeptide Y neuroactivity and decreased thermogenesis occur. Naltrexone is an opioid receptor antagonist which decreases neuropeptide Y-induced feeding and reverse neuropeptide Y-induced decreases in brown adipose tissue thermogenesis. We hypothesized that opioid receptors are involved in neuropeptide Y neuroactivity during lactation. To see if naltrexone would alter feeding neuropeptide Y gene expression in the arcuate nucleus, neuropeptide Y levels in the paraventricular nucleus, and uncoupling protein gene expression in brown adipose tissue of lactating rats, osmotic minipumps pre-filled with either 0.9% saline or naltrexone (70 micrograms/h) were implanted subcutaneously in 47 female Sprague-Dawley rats weighing 309 +/- 5 g. Half these rats were studied on days 10-16 of lactation, and the other half were studied 7 days after lactation. After 48 h, neuropeptide Y mRNA levels and uncoupling protein mRNA levels were determined using specific cDNA probes. Neuropeptide Y peptide levels in the paraventricular nucleus were measured by radioimmunoassay. Naltrexone decreased food intake by 26% in the postlactating rats, but had no effect on feeding in the lactating animals. Lactation resulted in significantly increased arcuate neuropeptide Y mRNA, decreased neuropeptide Y levels in the paraventricular nucleus and decreased brown adipose tissue uncoupling protein mRNA levels. Naltrexone did not influence any of these parameters. Thus, the alterations in neuropeptide Y neuroactivity and brown fat thermogenesis which occur in lactation is not altered by generalized opioid receptor blockade.

Opioids in the nucleus of the solitary tract are involved in feeding in the rat

We evaluated the effect of selective opioid peptides and naltrexone on feeding when injected into the nucleus of the solitary tract (NTS). Doses of 0, 1, 2, 4, and 8 nmol of [D-Ala2,N-Me-Phe4,Gly5-ol]enkephalin (DAMGO, mu-agonist), dynorphin A-(1-17) (DynA-(1-17), kappa-agonist), and [D-Ser2]leucine enkephalin-thr, (delta-agonist) were injected into the NTS in satiated male rats, and food intake was measured at 1, 2, and 4 h. Only DAMGO significantly increased feeding above control levels at doses of 2, 4, and 8 nmol. Doses of 10 and 50 microg naltrexone in the NTS significantly decreased 18-h deprivation-induced feeding. These data suggest that NTS opioid receptors (primarily mu) may be involved in the regulation of feeding.

Characterization of DinR, the Bacillus subtilis SOS repressor

In Bacillus subtilis, exposure to DNA damage and the development of natural competence lead to the induction of the SOS regulon. It has been hypothesized that the DinR protein is the cellular repressor of the B. subtilis SOS system due to its homology to the Escherichia coli LexA transcriptional repressor. Indeed, comparison of DinR and its homologs from gram-negative and -positive bacteria revealed conserved structural motifs within the carboxyl-terminal domain that are believed to be important for autocatalysis of the protein. In contrast, regions within the DNA binding domain were conserved only within gram-negative or -positive genera, which possibly explains the differences in the sequence specificities between gram-negative and gram-positive SOS boxes. The hypothesis that DinR is the repressor of the SOS regulon in B. subtilis has been tested through overexpression, purification, and characterization of the DinR protein. Like E. coli LexA, B. subtilis DinR undergoes an autocatalytic reaction at alkaline pH at a siscile Ala91-Gly92 bond. The cleavage reaction can also be mediated in vitro under more physiological conditions by the E. coli RecA protein. By using electrophoretic mobility shift assays, we demonstrated that DinR interacts with the previously characterized SOS box of the B. subtilis recA gene, but not with sequences containing single base pair mutations within the SOS box. Together, these observations strongly suggest that DinR is the repressor of the SOS regulon in B. subtilis.

Naloxone administration following operant training of sucrose/water discrimination in the rat

The suppression of food intake observed following naloxone administration has often been ascribed to palatability or taste. Unfortunately, many confounds become apparent when attempts are made to isolate such factors in the investigation of ingestive behaviors. In the present study, rats (two groups) were trained to discriminate either a 10% or 5% sucrose solution from water (0.1 ml). These mildly food deprived subjects (95% of free-feeding weight) were trained to press the appropriate lever in a two-lever operant chamber following sampling of sucrose or water; successful responding was reinforced by delivery of a 45 mg grain food pellet. Following random exposure to reduced sucrose concentrations tested under extinction, a sucrose concentration gradient (1.0, 0.5, 0.1, 0.05, 0.01 and 0.005% sucrose solution) was established for both training groups under i.p. saline administration. Data collected under i.p. saline were then compared to those collected following random i.pf1p4loxone administration (3.0, 1.0, 0.3 and 0.1 mg/kg). No significant differences were observed between the sucrose concentration gradients obtained under saline and those obtained under naloxone, suggesting that the anorectic effect of naloxone is not primarily determined by discrimination of sweet taste.

Why do we eat? A neural systems approach

Neuroregulators found at various brain sites are involved in controlling food intake, a behavior that occurs for many reasons. Different neuroregulators may affect different stimuli that impact eating behavior. For example, neuropeptide Y may initiate feeding for energy needs, opioid peptides may provide the rewarding aspects of eating, and corticotropin releasing factor may affect stress-induced eating. We know that the neural networks regulating feeding also impact other components of energy balance. Neuropeptide Y not only increases eating, it also decreases energy expenditure in brown fat and increases enzymatic activity associated with fat storage in white fat, resulting in a more obese animal. What the sites of action are of these neuroregulators and how they interact with regulators at other sites are of utmost importance. Different regions of the brain, together with the periphery, communicate via signals acting in coordinated fashion, which leads to the final outcome: eating less or more and expending less or more energy.

Orphanin FQ, agonist of orphan opioid receptor ORL1, stimulates feeding in rats

It has long been known that opioids, whether administered exogenously or released endogenously, play a role in feeding behavior, and that blockade of opioid receptors with various antagonists can inhibit feeding. Recently, the orphan opioid receptor, ORL1, and its presumed ligand, orphanin FQ, have been identified in human and rodent brain, and show structural similarity to classical opioid receptors and peptides, respectively. While it has been shown that central administration of orphanin FQ induces hyperalgesia, the effects of this peptide on food intake have not been studied. In the present study, we report that central injection of orphanin FQ induces feeding in satiated rats and that this effect can be blocked by peripheral administration of the opioid antagonist naloxone.

The UmuD' protein filament and its potential role in damage induced mutagenesis

BACKGROUND

Damage induced 'SOS mutagenesis' may occur transiently as part of the global SOS response to DNA damage in bacteria. A key participant in this process is the UmuD protein, which is produced in an inactive from but converted to the active form, UmuD', by a RecA-mediated self-cleavage reaction. UmuD', together with UmuC and activated RecA (RecA*), enables the DNA polymerase III holoenzyme to replicate across chemical and UV induced lesions. The efficiency of this reaction depends on several intricate protein-protein interactions.

RESULTS

Recent X-ray crystallographic analysis shows that in addition to forming molecular dimers, the N- and C-terminal tails of UmuD' extend from a globular beta structure to associate and produce crystallized filaments. We have investigated this phenomenon and find that these filaments appear to relate to biological activity. Higher order oligomers are found in solution with UmuD', but not with UmuD nor with a mutant of UmuD' lacking the extended N terminus. Deletion of the N terminus of UmuD' does not affect its ability to form molecular dimers but does severely compromise its ability to interact with a RecA-DNA filament and to participate in mutagenesis. Mutations in the C terminus of UmuD' result in both gain and loss of function for mutagenesis.

CONCLUSIONS

The activation of UmuD to UmuD' appears to cause a large conformational change in the protein which allows it to form oligomers in solution at physiologically relevant concentrations. Properties of these oligomers are consistent with the filament structures seen in crystals of UmuD'.

Identification of a DinB/UmuC homolog in the archeon Sulfolobus solfataricus

To date, eight closely related homologs of the Escherichia coli UmuC protein have been identified. All of these homologs appear to play critical roles in damage-inducible mutagenesis in enterobacteriaceae. Recently, a distantly related UmuC-homolog, DinB, has also been identified in E. coli. Using the polymerase chain reaction together with degenerate primers designed against conserved regions found in UmuC-like proteins, we have identified a new member of the UmuC-superfamily in the archeon Sulfolobus solfataricus. This new homolog shows high sequence similarity to DinB and a lower level of similarity to UmuC. As a consequence, we have called this new gene dbh (dinB homolog). Analysis of approximately 2.7 kb DNA encompassing the dbh region revealed several open reading frames (orfs). One, encoding a putative ribokinase, was located immediately upstream of dbh. This orf overlaps the dbh gene by 4 bp suggesting that both proteins might be coordinately expressed. Further upstream of the ribokinase-dbh locus was another orf encoding a potential ATPase homologous to two uncharacterized S. cerevisiae proteins (YD9346.02c and SC38KCXVI_20) and another E. coli DNA repair protein, RuvB. While this is the first report of a UmuC-like homolog in an archeon, we detected additional homologs using protein sequence comparisons in Gram-positive bacteria, cyanobacteria, and among potential human EST products, indicating that UmuC-related proteins comprise a ubiquitous superfamily of proteins probably involved in DNA repair and mutagenesis.

Oncogene alterations in primary, recurrent, and metastatic human bone tumors

We investigated the structure and the expression of various oncogenes in three of the most common human bone tumors-osteosarcoma (36 samples from 34 patients), giant cell tumor (10 patients), and chondrosarcoma (18 patients)-in an attempt to identify the genetic alterations associated with these malignancies. Alterations of RB and p53 were detected only in osteosarcomas. Alterations of c-myc, N-myc, and c-fos were detected in osteosarcomas and giant cell tumors. Ras alterations (H-ras, Ki-ras, N-ras) were rare. Chondrosarcomas did not contain any detectable genetic alterations. Our results suggest that alterations of c-myc, N-myc, and c-fos oncogenes occur in osteosarcomas, in addition to those previously described for the tumor suppressor genes RB and p53. Moreover, statistical analyses indicate that c-fos alterations occur more frequently in osteosarcoma patients with recurrent or metastatic disease.

Regulation of SOS mutagenesis by proteolysis

DNA damage-inducible mutagenesis in Escherichia coli is largely dependent upon the activity of the UmuD (UmuD') and UmuC proteins. The intracellular level of these proteins is tightly regulated at both the transcriptional and the posttranslational levels. Such regulation presumably allows cells to deal with DNA damage via error-free repair pathways before being committed to error-prone pathways. We have recently discovered that as part of this elaborate regulation, both the UmuD and the UmuC proteins are rapidly degraded in vivo. We report here that the enzyme responsible for their degradation is the ATP-dependent serine protease, Lon. In contrast, UmuD' (the posttranslational product and mutagenically active form of UmuD) is degraded at a much reduced rate by Lon, but is instead rapidly degraded by another ATP-dependent protease, ClpXP. Interestingly, UmuD' is rapidly degraded by ClpXP only when it is in a heterodimeric complex with UmuD. Formation of UmuD/UmuD' heterodimers in preference to UmuD' homodimers therefore targets UmuD' protein for proteolysis. Such a mechanism allows cells to reduce the intracellular levels of the mutagenically active Umu proteins and thereby return to a resting state once error-prone DNA repair has occurred. The apparent half-life of the heterodimeric UmuD/D' complex is greatly increased in the clpX::Kan and clpP::Kan strains and these strains are correspondingly rendered virtually UV non-mutable. We believe that these phenotypes are consistent with the suggestion that while the UmuD/D' heterodimer is mutagenically inactive, it still retains the ability to interact with UmuC, and thereby precludes the formation of the mutagenically active UmuD'2C complex.