Characterization of Neurospora mitochondrial group I introns reveals different CYT-18 dependent and independent splicing strategies and an alternative 3' splice site for an intron ORF

The Neurospora crassa mitochondrial tyrosyl-tRNA synthetase (CYT-18 protein) functions in splicing the N. crassa mitochondrial large rRNA intron by stabilizing the catalytically active structure of the intron core. Here, a comprehensive study of N. crassa mtDNA group I introns identified two additional introns, cob-I2 and the ND1 intron, that are dependent on CYT-18 for splicing in vitro and in vivo. The other seven N. crassa mtDNA group I introns are not CYT-18-dependent and include five that self-splice and two that do not splice under any conditions examined. Some of these introns may require maturases or other proteins for efficient splicing. All but one of the non-CYT-18-dependent introns contain large peripheral extensions of the P5 stem, related to the P5abc structure that blocks CYT-18 binding to the Tetrahymena large rRNA intron. The remaining non-CYT-18-dependent intron, cob-I1, contains a long, peripheral extension of the P9 stem, denoted P9.1, which also impedes CYT-18 binding. Detailed analysis of the CYT-18-dependent ND1 intron showed that two 3' splice sites are used in vitro and in vivo. The proximal, alternative 3' splice site brings the intron open reading frame, which potentially encodes a mobility endonuclease, in frame with the upstream exon, possibly providing a means of expression. Considered together, our results show that group I introns in N. crassa mitochondria use a variety of strategies involving different proteins and/or RNA structures to assist splicing, and they support the hypothesis that CYT-18 and the peripheral RNA structure P5abc are alternative evolutionary adaptations for stabilizing the active structure of the intron core.

Cloning and characterization of the Neurospora crassa cyt-5 gene. A nuclear-coded mitochondrial RNA polymerase with a polyglutamine repeat

The Neurospora crassa mutants, cyt-5-1 and cyt-5-4 have a cytochrome b- and aa3-deficient phenotype, suggesting that they result from a deficiency in a nuclear-coded component of the mitochondrial gene expression apparatus (Bertrand, H., Nargang, F. E., Colllins, R. A., and Zagozeski, C. A. (1977) Mol. Gen. Genet. 153,247-257). The complementing wild-type gene has been cloned and and shown to encode a protein with significant sequence similarity to Saccharomyces cerevisiae mitochondrial RNA polymerase and bacteriophage RNA polymerases. There are remarkable differences between the N. crassa protein and its yeast homologue, including a region of very little homology near the N termini of the two gene products. The cyt-5 gene encodes a stretch of polyglutamine in this region of uniquesequence. In addition, an acidic insertion (86 amino acids, of which 24 are Asp or Glu and 10 are Arg or Lys) is present near the C terminus of the cyt-5 gene product. Transcript levels of the cytochrome b and cytochrome oxidase subunit III genes are severely reduced in cyt-5 mutants, suggesting a likely mechanism for the cytochrome-deficient phenotype. In contrast, mitochondrial rRNAs accumulate to nearly normal levels in cyt-5 mutants. However, mitochondrial rRNA levels are not indicative of the rate of transcription of the corresponding genes, since crude lysates of mitochondria from cyt-5 mutants exhibit greatly reduced transcriptional activity with a 19 S rRNA promoter. The cyt-5 gene is flanked by at least one gene whose product also may be involved in mitochondrial function.

Posttranslational modification of glyceraldehyde-3-phosphate dehydrogenase by S-nitrosylation and subsequent NADH attachment

Nitric oxide (NO)-related activity has been associated with an NAD+-dependent modification of the glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase (GAPDH). However, the mechanism by which NO effects covalent attachment of nucleotide and its role in regulation of enzyme activity are controversial. Recent studies have shown that S-nitrosylation of GAPDH (Cys149) initiates subsequent modification by the pyridinium cofactor. Here we show that NADH rather than NAD+ is the preferred substrate. Transnitrosation from active site S-nitrosothiol to the reduced nicotinamide ring system appears to facilitate protein thiolate attack on the enzyme-bound cofactor. This results in attachment of the intact NADH molecule. Moreover, we find that S-nitrosylation of GAPDH is responsible for reversible enzyme inhibition, whereas attachment of NADH accounts for irreversible enzyme inactivation. S-Nitrosylation may serve to protect GAPDH from oxidant inactivation in settings of cytokine overproduction and to regulate glycolysis. NADH attachment is more likely to be a pathophysiological event associated with inhibition of gluconeogenesis.

The VS catalytic RNA replicates by reverse transcription as a satellite of a retroplasmid

The mitochondria of certain natural isolates of Neurospora contain both the Varkud plasmid, which encodes a reverse transcriptase, and a small unrelated RNA (VS RNA) that performs RNA-mediated self-cleavage and ligation reactions. Here, we show that VS RNA is transcribed from a VS plasmid DNA template by the Neurospora mitochondrial RNA polymerase using a promoter located immediately upstream of the RNA self-cleavage site that generates monomeric transcripts. VS RNA is then reverse transcribed by the Varkud plasmid reverse transcriptase to yield a full-length (-) strand cDNA, a predicted replication intermediate. Combined with previous genetic evidence, our results indicate that the VS plasmid replicates by reverse transcription as a satellite of the Varkud plasmid. This mode of replication, unprecedented for a satellite RNA, likely reflects the promiscuity of the Varkud plasmid reverse transcriptase, which does not require a specific primer to initiate cDNA synthesis. Our findings indicate how primitive reverse transcriptases with similar relaxed specificity could have facilitated the evolution of new retroelements.

Activin A and retinoic acid synergize in cyclooxygenase-1 and thromboxane synthase induction during differentiation of J774.1 macrophages

The murine macrophage cell line J774.1 was used to study the development of prostanoid biosynthesis under the influence of activin A and retinoic acid. Treatment of cells with 3 nM activin A for 48 h increased the biosynthesis of the prostaglandins E2, D2, F2 alpha and thromboxane A2 more than fourfold due to an induction of cyclooxygenase-1 while cyclooxygenase-2 was unaffected. Transforming growth factor-beta acted in a similar way. Retinoic acid, when present alone, was without effect on the total cyclooxygenase products and only slightly changed the pattern of prostanoids. However, when coincubated with activin A, retinoic acid specifically induced the synthesis of thromboxane-A-synthase-specific mRNA and induced an increase in enzyme activity with a synergistic effect on cyclooxygenase-1 protein and mRNA. JunB, but not c-jun, mRNA expression was found under these conditions in addition to a transient c-fos mRNA increase. The combination of activin A and retinoid acid may be regarded as a differentiation model to study the development of cell-specific prostanoid patterns in macrophages and possibly other differentiating cells.

Protein thiol modification and apoptotic cell death as cGMP-independent nitric oxide (NO) signaling pathways

Nitric oxide signaling is achieved through both cGMP-dependent and cGMP-independent mechanisms. The latter are exemplified by protein thiol modification followed by subsequent NAD(+)-dependent automodification of the glycolytic enzyme GAPDH, or by mechanisms inducing accumulation of the tumor suppressor gene p53 and causing apoptotic cell death. Both cGMP-independent actions are initiated using NO-releasing compounds and an active LPS/cytokine-inducible NO synthase. NO-synthase inhibitors block the release of NO and hinder downstream signaling mechanisms; they are therefore valuable pharmacological tools linking a defined cellular response to various NO actions. Signal transducing mechanisms elicited by NO can be studied using GAPDH as a representative example of NO-induced protein modification and are grouped as follows: --S-Nitrosylation reactions initiated by NO+ --NAD(+)-dependent, post-translational covalent automodification of GAPDH --Oxidative modification (thiol oxidation) and inhibition of GAPDH by NO-related agents, probably ONOO- GAPDH and several other protein targets may serve as molecular sensors of elevated NO concentrations and may transmit this message through posttranslational modification and oxidation-induced conformational changes as cGMP-independent NO signaling pathways. Toxicity of NO seems to be linked to both apoptosis and necrosis, depending on the chemistry of NO it undergoes in a given biological milieu. Toxicity manifests as a relative excess of NOx, metal-NO interactions, and ONOO- formation in relation to cellular defense systems. Although accumulation of the tumor-suppressor gene product p53 in response to NO opens a regulatory mechanism known to be involved in apoptotic cell death, cGMP-independent signaling pathways remain to be elucidated. As NO-dependent modification of GAPDH would imply down-regulation of glycolysis and concomitant energy production followed by cell death, our data so far do not support this assumption. In recent years, NO has proved to be a beneficial messenger with a potentially toxic activity. It will be challenging to investigate NO biochemistry in closer detail and to elucidate how NO targets biological systems, especially in relation to its pathophysiological role.

Raynaud's phenomenon associated with the use of pneumatically powered surgical instruments

Five patients developed symptoms of Raynaud's phenomenon and upper extremity paresthesias after 7-32 months of exposure to air-powered surgical instruments used for the harvest of bone for bone banks. Results of cold challenge plethysmography, nerve conduction studies, vibrotactile thresholds, and quantitative sensory testing were as follows: all patients had significant reproducible vasospasm with nondetectable finger systolic blood pressure (FSBP = 0) after local digital cooling; nerve conduction abnormalities included delayed median nerve sensory conduction (< 48 m/s) across 5 of 10 wrists; and no ulnar nerve abnormalities were detected. Vibrotactile thresholds were only modestly elevated, an unexpected outcome given the frequently recognized association between vibrotactile tests and nerve conduction studies. These abnormalities occurred with exposures to frequencies previously thought to be too high to be harmful to medical personnel.

Mechanism of covalent modification of glyceraldehyde-3-phosphate dehydrogenase at its active site thiol by nitric oxide, peroxynitrite and related nitrosating agents

Previous studies have suggested that glyceraldehyde-3-phosphate dehydrogenase (GAPDH) undergoes covalent modification of an active site thiol by a NO.-induced [32P]NAD(+)-dependent mechanism. However, the efficacy of GAPDH modification induced by various NO donors was found to be independent of spontaneous rates of NO. release. To further test the validity of this mechanism, we studied the effects of nitrosonium tertrafluoroborate (BF4NO), a strong NO+ donor. BF4NO potently induces GAPDH labeling by the radioactive nucleotide. In this case, the addition of thiol significantly attenuates enzyme modification by competing for the NO moiety in the formation of RS-NO. Peroxynitrite (ONOO-) also induces GAPDH modification in the presence of thiol, consistent with the notion that this species can transfer NO+ (or NO2+) through the intermediacy of RS-NO. However, the efficiency of this reaction is limited by ONOO- -induced oxidation of protein SH groups at the active site. ONOO- generation appears to account for the modification of GAPDH by SIN-1. Thus, S-nitrosylation of the active site thiol is a prequisite for subsequent post-translational modification with NAD+, and emphasizes the role of NO+ transfer in the initial step of this pathway. Our findings thus provide a uniform mechanism by which nitric oxide and related NO donors initiate non-enzymatic ADP-ribosylation (like) reactions. In biological systems, endogenous RS-NO are likely to support the NO group transfer to thiol-containing proteins.

Mitochondrial DNA of cytoplasmic male-sterile Triticum timopheevi: rearrangement of upstream sequences of the atp6 and orf25 genes

The organization of mitochondrial DNA (mtDNA) and transcript patterns of the atp6 and orf25 genes were examined in cytoplasmic male-sterile (CMS) and fertile Triticum lines. Major differences are observed between CMS T. timopheevi and fertile T. aestivum for both mitochondrial genes. The T. aestivum mt genome carries two atp6 gene copies, whereas only a single copy of the atp6 gene is present in T. timopheevi mtDNA. Sequence data suggest that identical sequences upstream of the atp6 gene and the orf25 gene are involved in homologous recombination in both cytoplasms. The differences in the upstream sequences of the atp6 or the orf25 genes affect transcript sizes in both cytoplasms. Transcription initiation may occur at conserved promoter elements located at variable distances upstream of the aminoacid coding sequences. The correlation between the gene rearrangements and the CMS phenomenon in T. timopheevi is discussed.

Assessment of hepatic function. Comparison of caffeine clearance in serum and saliva during the day and at night

Hepatic microsomal function was assessed by a caffeine clearance test at night and during the day using saliva and serum samples obtained simultaneously. In 26 patients with cirrhosis, 21 patients with noncirrhotic liver disease and 15 control subjects caffeine elimination correlated well during the day and at night (r = 0.915 for serum and 0.917 for saliva). The correlation coefficients for caffeine clearance in saliva and serum were 0.940 during the day and 0.963 overnight. In the cirrhotic patients, clearance differed significantly from noncirrhotic liver disease and controls in saliva samples overnight: 0.51 +/- 0.45 ml/min per kg versus 0.91 +/- 0.44 and 1.41 +/- 0.56, respectively. Comparable results were obtained for serum clearance overnight and clearances during the day. Serum and saliva clearances at night correlated well with the aminopyrine breath test (rs = 0.884 and 0.907, respectively). Overnight caffeine clearance in saliva might be a simple useful method for assessing progression and prognosis of liver disease.

[Population exposure to pollutants--selected examples from Schleswig-Holstein]

Environmental health policy aims at protecting human health against toxic, cancerogenic, mutagenic, teratogenic and other damaging influences. Environmental toxicology must assess the risk of environmental pollutants by monitoring exposure, characterising hazards, and proposing preventive measures. Examples of the cooperation between Public Health departments and the Bureau of Environmental Toxicology of Slesvig-Holstein are presented.

Stage D1 adenocarcinoma of prostate

The natural history of Stage D1 adenocarcinoma of the prostate remains unclear. In a series of 50 patients with positive pelvic lymph nodes at the time of staging lymphadenectomy, metastatic disease developed in 43 per cent of the patients treated for cure within the period of time of follow-up. Several series from the literature confirm those findings. Positive pelvic lymph nodes most probably represent systemic disease, and the patients are incurable by current surgical and radiotherapeutic modalities.

Acid phosphatase: its influence on the management of carcinoma of the prostate

Of 343 patients who underwent pelvic lymph node dissection during treatment for carcinoma of the prostate 25 had persistently elevated serum enzymatic acid phosphatase levels preoperatively: 15 (60 per cent) had metastases to the pelvic lymph nodes and 10 (40 per cent) had negative nodes. Bone metastases occurred in 10 of 12 (83 per cent) and 5 of 7 patients (71 per cent), respectively, who were followed for a minimum of 2 years. Of the 318 patients with normal serum enzymatic phosphatase levels 70 (22 per cent) had positive nodes. A persistently elevated serum enzymatic acid phosphatase level in patients with proved carcinoma of the prostate, with elimination of infrequent causes of enzyme elevation, indicates metastases and has significant implications regarding staging and, thus, therapy of this disease.

Stroke risk from symptomless extracranial arterial disease

The natural history of a prospectively selected group of neurologically symptomless patients with extracranial arterial disease (EAD) was studied. 23 of 122 patients died over a period of follow-up of from eleven to thirty-six months (mean = seventeen), but only 3 from stroke and 10 from cardiac failure. Among those patients still alive 8 reported transient ischaemic attacks, 1 a stroke, and 90 remain symptomless. Thus, by life-table analysis, the cumulative stroke rate was only 7%, irrespective of death or survival, the same as the average risk of death in a normal population. However, by subsequent continuous-wave Doppler examination of carotid and vertebral arteries, the probability of EAD progression was 85%. Involvement of initially unaffected arteries occurred either alone (25) or in combination with a deterioration of the original stenosis (14)--the latter alone was seen in 9 patients. A combined carotid and vertebral lesion was found to be the only significant indicator of cerebrovascular risk, which was six times greater than that for unilateral or bilateral carotid lesions.

Perineal neoplasms

Experience with 2 cases of neurally-derived perineal masses is described. A relevant review of the literature spanning 50 years revealed 36 cases of perineal neoplasm of diverse nature, disclosing that such lesions typically present as otherwise asymptomatic enlarging masses and may comprise a broad spectrum of neoplasia with diagnosis and prognosis often relating to the age of the patient. Management naturally relates to tissue type and degree of local involvement.