recA (Srf) suppression of recF deficiency in the postreplication repair of UV-irradiated Escherichia coli K-12

The mechanism by which recA (Srf) mutations (recA2020 and recA801) suppress the deficiency in postreplication repair shown by recF mutants of Escherichia coli was studied in UV-irradiated uvrB and uvrA recB recC sbcB cells. The recA (Srf) mutations partially suppressed the UV radiation sensitivity of uvrB recF, uvrB recF recB, and uvrA recB recC sbcB recF cells, and they partially restored the ability of uvrB recF and uvrA recB recC sbcB recF cells to repair DNA daughter-strand gaps. In addition, the recA (Srf) mutations suppressed the recF deficiency in the repair of DNA double-strand breaks in UV-irradiated uvrA recB recC sbcB recF cells. The recA2020 and recA801 mutations do not appear to affect the synthesis of UV radiation-induced proteins, nor do they appear to produce an altered RecA protein, as detected by two-dimensional gel electrophoresis. These results are consistent with the suggestion (M. R. Volkert and M. A. Hartke, J. Bacteriol. 157:498-506, 1984) that the recA (Srf) mutations do not act by affecting the induction of SOS responses; rather, they allow the RecA protein to participate in the recF-dependent postreplication repair processes without the need of the RecF protein.

Myocardial high-energy phosphate levels in cardiomyopathic turkeys

A congestive cardiomyopathy (CCM) model occurs in inbred broad-breasted turkeys and is manifested by reduced hatchability and a high mortality within a week of hatching. In the survivors, cardiac dilation begins by 3-4 weeks of age and further mortality occurs from chronic congestive heart failure. The mechanisms behind these changes is unknown, and, therefore, we investigated what role, if any, myocardial energy metabolism might play in these events. Ventricular myocardial samples were obtained for analysis of adenine nucleotides (ATP, ADP, AMP) and creatine phosphate (CP) in control and CCM turkeys, 1-31 days old. The adenine nucleotide energy charge (EC) was calculated using the formula EC = ATP + 1/2ADP/(ATP + ADP + AMP). We found the myocardial ATP levels and EC in CCM hearts at 1-2 days were reduced. In control turkeys, no significant age-related differences were found in myocardial high-energy phosphate compounds or in the EC. This depression in the energy metabolism of CCM turkeys may also be reflected in their poor hatchability. By 6-10 days, however, ATP levels had recovered and remained normal despite the onset of cardiac dilation and failure at 3-4 weeks of age in CCM turkeys. Because CP levels in control and CCM turkey hearts were similar in all age groups, significant ischemia did not appear to be present after hatching in CCM turkeys. Our results suggest, therefore, that an insult probably prior to hatching produced depressed myocardial energy levels in CCM turkeys and led to reduced hatchability. This early insult appears to be significant, in that late cardiac dysfunction resulted despite the recovery of myocardial ATP levels.

Postreplication repair in ultraviolet-irradiated human fibroblasts: formation and repair of DNA double-strand breaks

A neutral filter elution assay was used to determine if the postreplicational formation and repair of DNA double-strand breaks (DSB) occurs in u.v.-irradiated human cells. Excision-deficient XP12 cells were pulse-labeled with [3H]thymidine after u.v. irradiation (1.5-3 J/m2), and the nascent DNA was followed during repair incubation. With increasing u.v. radiation fluences, an increasing fraction of DNA was eluted at a fast rate, indicating that DSB were produced. The maximum yield of DSB was observed after about 24 h of postirradiation incubation at 37 degrees C. Similar results were also obtained with repair-proficient VA13 cells when irradiated at much higher fluences (7.5-15 J/m2). It is concluded that, at the u.v. radiation fluences used in this work, the DSB produced in u.v.-irradiated human cells are the result of post-replication repair events, and at incubation times greater than 24 h some of these DSB are repaired.

Inviability of dam recA and dam recB cells of Escherichia coli is correlated with their inability to repair DNA double-strand breaks produced by mismatch repair

The molecular basis for the inviability of dam-3 recA200(Ts) and dam-3 recB270(Ts) cells was studied. The dam-3 recA200(Ts) cells were inviable in yeast extract-nutrient broth or in minimal medium at 42 degrees C. Although the dam-3 recB270(Ts) cells were inviable in yeast extract-nutrient broth at 42 degrees C, they were viable at 42 degrees C in minimal medium, in which the high salt content suppresses the mutant phenotype caused by the recB270(Ts) mutation at 42 degrees C. Under the growth conditions rendering dam rec cells inviable, the cells accumulated double-strand breaks in their DNA. Introduction of a mutL or mutS mutation restored the viability of dam-3 recB270(Ts) cells grown in yeast extract-nutrient broth at 42 degrees C and eliminated the formation of DNA double-strand breaks in these cells. We conclude that the inability to repair DNA double-strand breaks produced by the mismatch repair process accounts for the inviability of the dam recA and dam recB cells.

Postreplicational formation and repair of DNA double-strand breaks in UV-irradiated Escherichia coli uvrB cells

The number of DNA double-strand breaks formed in UV-irradiated uvrB recF recB cells correlates with the number of unrepaired DNA daughter-strand gaps, and is dependent on DNA synthesis after UV-irradiation. These results are consistent with the model that the DNA double-strand breaks that are produced in UV-irradiated excision-deficient cells occur as the result of breaks in the parental DNA opposite unrepaired DNA daughter-strand gaps. By employing a temperature-sensitive recA200 mutation, we have devised an improved assay for studying the formation and repair of these DNA double-strand breaks. Possible mechanisms for the postreplication repair of DNA double-strand breaks are discussed.

Vascular metatarsophalangeal to ankylosed temporomandibular joint replacement

Four cases of unilateral temporomandibular (TM) joint ankylosis were successfully treated by metatarsophalangeal to TM joint replacement by microvascular technique. Results 6 to 20 months postoperatively were encouraging. Further follow-up studies are necessary to evaluate the long-term results.

Mechanism of sbcB-suppression of the recBC-deficiency in postreplication repair in UV-irradiated Escherichia coli K-12

The mechanism by which an sbcB mutation suppresses the deficiency in postreplication repair shown by recB recC mutants of Escherichia coli was studied. The presence of an sbcB mutation in uvrA recB recC cells increased their resistance to UV radiation. This enhanced resistance was not due to a suppression of the minor deficiency in the repair of DNA daughter-strand gaps or to an inhibition of the production of DNA double-strand breaks in UV-irradiated uvrA recB recC cells; rather, the presence of an sbcB mutation enabled uvrA recB recC cells to carry out the repair of DNA double-strand breaks. In the uvrA recB recC sbcB background, a mutation at recF produced a huge sensitization to UV radiation, and it rendered cells deficient in the repair of both DNA daughter-strand gaps and DNA double-strand breaks. Thus, an additional sbcB mutation in uvrA recB recC cells restored their ability to perform the repair of DNA double-strand breaks, but the further addition of a recF mutation blocked this repair capacity.

Role of the umuC gene in postreplication repair in UV-irradiated Escherichia coli K-12 uvrB

The role of the umuC gene product in postreplication repair was studied in UV-irradiated Escherichia coli K-12 uvrB cells. A mutation at umuC increased the UV radiation sensitivities of uvrB, uvrB recF, uvrB recB, and uvrB recF recB cells; it also increased the deficiencies in the repair of DNA daughter-strand gaps in these strains, but it did not affect the repair of DNA double-strand breaks that arose from unrepaired DNA daughter-strand gaps. We suggest that the umuC gene product is involved in a minor system for the repair of DNA daughter-strand gaps, possibly the repair of overlapping DNA daughter-strand gaps.

Mechanisms for recF-dependent and recB-dependent pathways of postreplication repair in UV-irradiated Escherichia coli uvrB

The molecular mechanisms for the recF-dependent and recB-dependent pathways of postreplication repair were studied by sedimentation analysis of DNA from UV-irradiated Escherichia coli cells. When the ability to repair DNA daughter strand gaps was compared, uvrB recF cells showed a gross deficiency, whereas uvrB recB cells showed only a small deficiency. Nevertheless, the uvrB recF cells were able to perform some limited repair of daughter strand gaps compared with a "repairless" uvrB recA strain. The introduction of a recB mutation into the uvrB recF strain greatly increased its UV radiation sensitivity, yet decreased only slightly its ability to repair daughter strand gaps. Kinetic studies of DNA repair with alkaline and neutral sucrose gradients indicated that the accumulation of unrepaired daughter strand gaps led to the formation of low-molecular-weight DNA duplexes (i.e., DNA double-strand breaks were formed). The uvrB recF cells were able to regenerate high-molecular-weight DNA from these low-molecular-weight DNA duplexes, whereas the uvrB recF recB and uvrB recA cells were not. A model for the recB-dependent pathway of postreplication repair is presented.

Effects of the ssb-1 and ssb-113 mutations on survival and DNA repair in UV-irradiated delta uvrB strains of Escherichia coli K-12

The molecular defect in DNA repair caused by ssb mutations (single-strand binding protein) was studied by analyzing DNA synthesis and DNA double-strand break production in UV-irradiated Escherichia coli delta uvrB strains. The presence of the ssb-113 mutation produced a large inhibition of DNA synthesis and led to the formation of double-strand breaks, whereas the ssb-1 mutation produced much less inhibition of DNA synthesis and fewer double-strand breaks. We suggest that the single-strand binding protein plays an important role in the replication of damaged DNA, and that it functions by protecting single-stranded parental DNa opposite daughter-strand gaps from nuclease attack.

Residence time and carbon dioxide scrubbing efficiency in life support systems

Residence time affects the CO2 absorption rate and CO2 absorption capacity of different CO2 absorbents used in an enclosed space. For a given CO2 contents in the air stream at any given environmental condition, there is a corresponding residence time between CO2 and the absorbent which results in the maximum CO2 absorption efficiency. Different porosities for lithium hydroxide, Sodasorb, and Baralyme granules were studied. The residence time effects on the CO2 absorption patterns and CO2 absorption capacities were observed. Lithium hydroxide and the highest CO2 absorption capacity when the residence time was about 0.8 s. The CO2 absorption capacity of both Sodasorb and Baralyme was increased as residence time increased. However, when the residence time was less than 1.0 s, the CO2 absorption capacity of both absorbents was greatly reduced.

Residues of polychlorinated biphenyls and DDT in water and sediment of the St. Lucie Estuary, Florida, 1977

sigma DDT residues in the St. Lucie River bottom sediments increased after Lake Okeechobee water was discharged through the St. Lucie Canal into the area. sigma DDT levels were highest in sediment samples from the Palm City area, ranging from 1.8 ppb to 6.15 ppb. Sediment samples from the A1A Highway Bridge area contained 1.6-6.8 ppb Aroclor 1254. Levels of polychlorinated biphenyls (PCBs) and sigma DDT in sediment samples from the junction of the St. Lucie and Indian Rivers were not detectable. Surface water samples from the estuary did not show any detectable DDT or PCB residues.

Adaptation to cycloheximide of macromolecular synthesis in Tetrahymena

Cycloheximide (CHI) at 10 ng/ml partially inhibited protein synthesis in exponential cultures of Tetrahymena Sp. At 20 ng/ml or greater, inhibition was complete. When protein synthesis was inhibited to any extent, cell division ceased immediately. In all instances where measured, synthesis of RNA and DNA also ceased. After a period of delay, cellular functions reinitiated in the order: (i) protein synthesis, (ii) DNA synthesis and, (iii) RNA synthesis and cell division. The delay in cell division was divided into three phases of: I, zero; II, low; and, III; fully recovered rates of exponential protein synthesis. The length of the three phases increased with increasing concentration of CHI. Prior growth of cells for one generation in the presence of 7.5 ng/ml CHI (facilitation) eliminated phase I and slightly decreased phases II and III following subsequent challenge with an inhibitory concentration of CHI. Facilitation for six generations further decreased phases II and III. Protein synthesis and cell division were not inhibited during facilitation. In the culture, succinate dehydrogenase activity did not increase during the delay but increased normally at the onset of division. In contrast, NADPH-cytochrome c reductase activity continued to increase for an hour after inhibition of protein synthesis, was constant for a period and did not increase again until an hour after reinitiation of cell division and RNA synthesis. Inhibition of division of all cells was immediate and reinitiation of synthesis and cell division was non-synchronous.

Transitory germinative excision repair in Bacillus subtilis

Bacillus subtilis strains UVSSP-42-1 (hcr42 ssp1) and UVSSP-1-1 (hcr1 ssp1) are ultraviolet (UV) radiation sensitive both as dormant spores and as vegetative cells. These strains are unable to excise cyclobutane-type dimers from the deoxyribonucleic acid (DNA) of irradiated vegetative cells and fail to remove spore photoproduct from the DNA of irradiated spores either by excision (controlled by gene hcr) or by spore repair (controlled by gene ssp1). When irradiated soon after spore germination, these strains excise dimers, but not spore photoproduct, from their DNA. This process, termed germinative excision repair, functions only transiently in the germination phase and is responsible for the high UV resistance of germinated spores and for their temporary capacity to host cell reactivate irradiated phages infecting them. The recA1 mutation confers higher UV sensitivity to the germinated spores, but does not interfere with dimer removal by germinative excision repair.