Polyarthritis in wild mice (Mus musculus) caused by Streptobacillus moniliformis

Mice trapped on farms in south-eastern Queensland had chronic abscessating osteoarthritides mainly involving the carpi and tarsi. Pleomorphic bacteria were shown by silver staining to be plentiful within lesions. Streptobacillus moniliformis was isolated from the joints, and streptobacillary polyarthritis was diagnosed. Other lesions observed included subcutaneous and hepatic abscesses.

Descriptive epidemiology of prostate cancer in metropolitan Detroit

BACKGROUND

The incidence of prostate cancer among US men increased more than five times over the past six decades. Black men in the United States now have the world's highest reported incidence of prostate cancer. The authors examined the distribution of prostate cancer in metropolitan Detroit from 1973 to 1989.

METHODS

Cases collected by the Metropolitan Detroit Cancer Surveillance System were used to calculate standardized age-adjusted rates of prostate cancer by race and stage and standardized age-specific rates for the age groups 60-69, 70-79 and 80 years and older. Over 24,000 cases involving black and white men were analyzed.

RESULTS

During 1973 to 1989, age-adjusted rates of prostate cancer diagnosed among white men doubled from 54.3 to 109.9 per 100,000 and those among black men increased by nearly 40% from 106.9 to 148.6 per 100,000. Average annual increases in age-adjusted rates for white and black men were 4.4 and 2.3%, respectively.

CONCLUSIONS

Age-adjusted rates of prostate cancer diagnosed among white men increased more rapidly than rates among black men during 1973 to 1989. The more rapid increase in cases diagnosed in white men may represent differences in access and exposure to early detection and treatment practices. Improved efforts toward earlier detection are needed, especially among black men.

Goldfish tyrosinase related protein I (TRP-1): deduced amino acid sequence from cDNA and comments on structural features

Previous workers have shown that mammals have tyrosinase and tyrosinase related proteins (TRPs) that share common structural domains, all of which are not present in microbial tyrosinases. We report here the deduced amino acid sequence of a TRP from fish that is highly homologous to mammalian TRP-1. Examination of the structures of these vertebrate tyrosinases and TRPs shows that, aside from the conserved cysteine-rich and histidine-rich domains previously noted, there are a large number of conserved prolines and glycines, leading to an abundance of turns and few conserved helical regions. These tyrosinases and TRP-1s also have in their cytosolic tails a consensus sequence that is not present in any other protein. It is proposed that this sequence may participate in directing these proteins to the melanosomes.

Changes in cultivar-specificity toward pea can result from transfer of plasmid RP4 and other incompatibility group P1 replicons to Pseudomonas syringae pv. pisi

Transfer of RP4 and related replicons belonging to the Escherichia coli incompatibility group P (Pseudomonas aeruginosa IncP1) to races 2 and 6 of P. syringae pv. pisi was associated with the creation of two types of transconjugant, one resembling the parental race and the other showing an altered cultivar-specificity towards pea. The latter, irrespective of the parental race, exhibited a novel pattern of interaction with pea that corresponded to race 4; consequently such transconjugants were termed race 4-like. Curing of RP4 did not affect the phenotype, except in relation to the antibiotic resistances specified by RP4. The race 4-like strains were non-fluorescent when cultured on appropriate media (in contrast to the particular isolates of races 2 and 6 from which they were derived), showed an enhanced ability to inherit RP4 subsequently (at frequencies up to 10(-1) per recipient) and differed from their parental race in their pattern of plasmid profile. The plasmid profiles were similar for all race 4-like strains irrespective of origin. There was no evidence that RP4 had recombined with DNA in the recipient and probing failed to detect the retention of any part of RP4 in cured strains. The inheritance of the related cosmid vector, pLAFR3, had similar effects in races 2 and 6. This observation is important since this vector has been widely used to clone avirulence genes in plant pathogenic bacteria. Transfer of the IncW plasmids S-a and R388 did not cause any changes in the fluorescence or cultivar-specificity of races 2 or 6.(ABSTRACT TRUNCATED AT 250 WORDS)

A CRE/ATF-like site in the upstream regulatory sequence of the human interleukin 1 beta gene is necessary for induction in U937 and THP-1 monocytic cell lines

Transfection of U937 and THP-1 cells with a recombinant plasmid, pIL1(4.0kb)-CAT, containing 4 kb of the interleukin 1 beta (IL-1 beta) gene upstream regulatory sequence resulted in inducer-dependent expression of chloramphenicol acetyltransferase activity. Treatment of the transfected cells with various combinations of the inducers lipopolysaccharide, phorbol myristate acetate, and dibutyryl cyclic AMP upregulated the IL-1 beta promoter. In U937 and THP-1 cells, maximum stimulation of both the endogenous IL-1 beta gene and pIL1(4.0kb)-CAT transfectants was observed following treatment with the combination of inducing agents lipopolysaccharide-phorbol myristate acetate-dibutyryl cyclic AMP. This combination of inducing agents was used to identify and study, at the molecular level, some of the regulatory elements necessary for induction of the IL-1 beta gene. A series of 5' deletion derivatives of the upstream regulatory sequence were used in transient transfection assays to identify an 80-bp fragment located between -2720 and -2800 bp upstream of the mRNA start site that was required for induction. Exonuclease III mapping, electrophoretic mobility shift assays (EMSA), and DNA sequence analysis of this region were used to identify a transcription factor binding sequence which contained a potential cyclic AMP response element (CRE/ATF)- and NF-kappa B-like binding site. Site-directed mutagenesis of the CRE/ATF-like site resulted in the loss of binding of a specific factor or factors as determined by EMSA. The loss of binding activity directly correlated with a loss of approximately 75% of promoter activity as determined in transient transfection assays. As determined by EMSA, the factor binding to the CRE/ATF-like site was present in nuclear extracts prepared from both uninduced and induced THP-1 and U937 cells. However, the intensity of the band appeared to be increased when nuclear extracts from induced cells were used. In contrast to the CRE/ATF mutation, which resulted in the loss of promoter activity, mutation of the NF-kappa B-like site resulted in a moderate increase in activity in U937 cells. A similar increase in promoter activity was not observed in THP-1 cells. From these studies, we conclude that a CRE/ATF-like site and a factor or factors interacting with this site are essential for the maximum induction of the IL-1 beta gene in stimulated U937 and THP-1 cells.

The lipoxygenase metabolite, 12(S)-HETE, induces a protein kinase C-dependent cytoskeletal rearrangement and retraction of microvascular endothelial cells

We previously reported that a lipoxygenase metabolite of arachidonic acid, 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE], induced large vessel endothelial cell (EC) retraction and increased tumor cell adhesion to exposed extracellular matrix (Honn et al., FASEB J. 3, 2285-2293, 1989). Here, we present evidence that 12(S)-HETE induces the retraction of microvascular ECs in a time- and concentration-dependent manner. The EC retraction was observed 15 min after 12(S)-HETE treatment and reached a peak level between 1 and 2 h. The monolayer reformed by 24 h. Silver staining and "gap-FRAP" experiments suggest that 12(S)-HETE altered the normally apposed cell junctions and impaired gap junction-mediated cell-cell communication. It appears that the 12(S)-HETE effect was mediated by cytoskeletal alteration. The first observed alteration in EC cytoskeleton following 12(S)-HETE stimulation is vimentin bundling, followed by the rearrangement and disruption of vinculin-containing adhesion plaques and/or simultaneous redistribution of alpha-actinin and disruption of spectrin. These changes are accompanied by progressive microfilament dissolution. During the same time interval, alpha-actinin is mobilized to the cell periphery at cell "ruffles." However, 12(S)-HETE showed little or no effects on actin-binding proteins filamin and tropomyosin or on microtubules. 12(S)-HETE effects on these cytoskeletal elements were fully reversible by 24 h and appeared to be mediated through enhancing protein phosphorylation. Following 12(S)-HETE (0.1 microM) treatment increased phosphorylation of proteins that comigrated with myosin light chain (20 kDa), actin (42 kDa), and vimentin (57 kDa) were observed. The enhanced phosphorylation of these cytoskeletal proteins was confirmed by 2D gel analysis. The phosphorylation-promoting effect of 12(S)-HETE on cytoskeletal proteins could be totally abolished by calphostin C, partially inhibited by staurosporine, but was not influenced by N-[2-(methylamine)ethyl]-5-isoquinolinesilfonamide dihydrochloride (HS), suggesting that the 12(S)-HETE effect was mediated via protein kinase C. This was further substantiated by quantitative experiments demonstrating that calphostin C, but not H8, inhibited 12(S)-HETE-induced EC retraction.

Phenotypic properties of cultured tumor cells: integrin alpha IIb beta 3 expression, tumor-cell-induced platelet aggregation, and tumor-cell adhesion to endothelium as important parameters of experimental metastasis

The present study was undertaken to investigate the factors involved in determining the metastatic potential of cultured cells derived from solid tumors. We first investigated the effects of cell source and culture conditions on lung colony formation by i.v. injected B16a (B16 amelanotic melanoma) cells and inhibition of tumor colony formation by the thromboxane A2 synthase inhibitor, CGS14854. Prolonged culture resulted in a 10-fold decrease in the incidence of B16a lung colonies, whereas passage in vivo for 150 days did not affect lung colony formation by tumor cells isolated from enzymatic dispersates by centrifugal elutriation. Cultured B16a cells maintained at low density (LD) and harvested at low passage (LP) formed significantly more lung colonies than B16a cells harvested at high densities (HD) or high passage (HP). Over-confluent tumor cells produced even lower number of lung colonies. Lung colony formation by elutriated B16a cells (i.e., cells freshly isolated from tumor tissue) was consistently inhibited by CGS14854, whereas inhibition of lung colony formation by cultured B16a cells was dependent upon culture conditions. CGS14854 was ineffective or less effective against HD/HP B16a cells. The differences in lung colony formation between LD, HD and elutriated B16a cells were not due to differential cell-cycle distribution. Mechanistic studies indicated that LD/LP tumor cells induced aggregation of homologous platelets, whereas HD/HP B16a cells failed to induce significant platelet aggregation. Aggregation of homologous platelets correlated positively with lung-colonizing ability. Additionally, LD/LP cells demonstrated higher adhesion to endothelium than HD/HP B16a cells. Finally, LD/LP B16a cells expressed higher levels of alpha IIb beta 3 integrins than HD/HP tumor cells, as determined by flow cytometry and immunofluorescence.

Iodine therapy for thyroidectomy patients exhibiting high thyroid-stimulating hormone values: a randomised study

After thyroidectomy there is an appreciable incidence of hypothyroidism as judged by FT4I estimates. Pharmacological doses of iodine (10-300 mg/day) usually suppress, whereas physiological doses of iodine (< 5 mg/day) have been reported to both decrease and increase thyroid function. The value of iodine supplementation in preventing post-thyroidectomy hypothyroidism was assessed in a prospective randomised trial. A series of 55 patients with a TSH > 6 mU/l 1 month after bilateral subtotal thyroidectomy or unilateral lobectomy for benign disease were randomised to receive either chloroform water 5 ml/day (placebo) or chloroform water 5 ml/day with 1 mg of iodine to be taken for 20 weeks. With placebo, 62% of bilateral subtotal thyroidectomies were euthyroid at 6 months on no thyroid replacement, while with iodine all were hypothyroid as judged by FT4I. After bilateral subtotal thyroidectomy, the recovery of remnant function is delayed by an iodine supplement of 1 mg/day.

Short-wavelength color visual fields in glaucoma suspects at risk

Glaucoma suspect eyes were seen during a five-year study on color visual fields that used a 440-nm test on a bright-yellow background (96 normal eyes, 55 suspect eyes, and 110 eyes that developed glaucoma). The predictive ability of the test was assessed in 25 eyes followed up for more than one year, five of which developed glaucoma. These five eyes and those at high risk showed higher mean defect (P < .0001) and number of defective points (P < .0001) than the other suspect groups, which were not significantly different from normal eyes. The mean defects (+/- standard deviations) and average number of defective points were 1.4 +/- 2.3 dB with 8.9 points (low-risk eyes), 1.1 +/- 1.2 dB with 8.0 points (medium-risk eyes), 6.7 +/- 2.8 dB with 27.7 points (high-risk eyes), and 9.3 +/- 1.8 dB with 39.4 points (eyes that developed glaucoma). Normal eyes had an average of 3.4 defective points. These results were similar when all 55 suspect eyes were analyzed. Color visual fields identify early functional loss in eyes at greatest risk for primary open-angle glaucoma.

PKC mediates 12(S)-HETE-induced cytoskeletal rearrangement in B16a melanoma cells

The fatty acid 12(S)-HETE may be a new second messenger capable of activating PKC. In tumor cells 12(S)-HETE stimulates cytoskeleton-dependent cellular responses such as adhesion and spreading. Analysis of 12(S)-HETE effects on B16a melanoma cell cytoskeleton revealed reversible rearrangement of microtubules, microfilaments, the actin-binding proteins, vinculin, myosin heavy (MHC) and light chains (MLC), as well as bundling of vimentin intermediate filaments. The alterations in microfilaments and intermediate filaments occurred very rapidly, i.e., 5 min after exposure of tumor cells to 12(S)-HETE. The 12(S)-HETE-induced cytoskeletal alterations were accompanied by centrifugal organelle-translocation. Interestingly, MLC exhibited clear association with the cytoplasmic organelles. Biochemical analysis of the 12(S)-HETE effect indicated a PKC-mediated reversible hyperphosphorylation of MLC, vimentin, and a 130 kD cytoskeletal-associated protein. Optimal effects were obtained after 5 min treatment with 12(S)-HETE at 0.1 microM concentration. 12(S)-HETE pretreatment induced tumor cell spreading on a fibronectin matrix which required the intactness of all three major cytoskeletal components. The spreading process was dependent upon the activity of PKC. Our data suggest that 12(S)-HETE is a physiological stimulant of PKC. Further, it induces rearrangement of the cytoskeleton of tumor cells in interphase resulting in the stimulation of cytoskeleton-dependent cell activity such as spreading.

Increased mitochondrial activities in pigmented (melanized) fish cells and nucleotide sequence of mitochondrial large rRNA

Using the subtracted probe approach, we had previously isolated eight cDNAs whose corresponding RNAs are more abundant in pigmented (melanized) than in closely related unpigmented goldfish cell lines. We report here that two of these are of mitochondrial origin, suggesting that pigmentation is accompanied by higher content (activity) of mitochondria. We also present the complete nucleotide sequence of the full length cDNA for the large mitochondrial rRNA, showing the presence of a polyA tail, two polyadenylation signals and a long open reading frame potentially encoding for a polypeptide of 166 amino acids and with no known protein homologue. It is however unknown whether such a polypeptide is actually produced.

Functional homologs of the Arabidopsis RPM1 disease resistance gene in bean and pea

We showed that a bacterial avirulence (avr) gene function, avrPpiA1, from the pea pathogen Pseudomonas syringae pv pisi, is recognized by some, but not all, genotypes of Arabidopsis. Thus, an avr gene functionally defined on a crop species is also an avr gene on Arabidopsis. The activity of avrPpiA1 on a series of Arabidopsis genotypes is identical to that of the avrRpm1 gene from P.s. pv maculicola previously defined using Arabidopsis. The two avr genes are homologous and encode nearly identical predicted products. Moreover, this conserved avr function is also recognized by some bean and pea cultivars in what has been shown to be a gene-for-gene manner. We further demonstrated that the Arabidopsis disease resistance locus, RPM1, conditioning resistance to avrRpm1, also conditions resistance to bacterial strains carrying avrPpiA1. Therefore, bean, pea, and conceivably other crop species contain functional and potentially molecular homologs of RPM1.

The lipoxygenase metabolite 12(S)-HETE promotes alpha IIb beta 3 integrin-mediated tumor-cell spreading on fibronectin

Tumor-cell interaction with the vessel wall during metastasis involves adhesion, induction of endothelial-cell retraction and spreading on the exposed sub-endothelial matrix. The signals for initiation of tumor-cell spreading and the receptors involved are unknown. A protocol was developed to distinguish between initial tumor-cell (B16 amelanotic melanoma; B16a) adhesion to and spreading on fibronectin. The time for maximum spreading was 50 min. Treatment with a lipoxygenase metabolite of arachidonic acid [12(S)-HETE] resulted in maximum spreading in 15 min (max. effect approx. 0.1 microM). Other lipoxygenase metabolites were ineffective. 12(S)-HETE treatment induced a rearrangement of F-actin, vinculin, vimentin intermediate filaments and integrin alpha IIb beta 3, but not integrin alpha 5 beta 1. Antibodies to alpha IIb beta 3 but not alpha 5 beta 1 blocked the 12(S)-HETE effect on B16a spreading. B16a-cell attachment to fibronectin resulted in increased metabolism of arachidonic acid to 12(S)-HETE, which was inhibited by lipoxygenase but not by cyclo-oxygenase inhibitors. Accordingly, lipoxygenase inhibitors but not cyclo-oxygenase inhibitors blocked spontaneous B16a-cell spreading. The protein-kinase-C inhibitors calphostin C, H7 and staurosporine also inhibited spreading, while the protein-kinase-A inhibitor H8 was ineffective. These data suggest that B16a-cell spreading on fibronectin is initiated by a lipoxygenase metabolite [12(S)-HETE] of arachidonic acid and is mediated by protein kinase C.

Identification of the alpha IIb beta 3 integrin in murine tumor cells

Previously, we have identified an alpha IIb beta 3-like integrin in tumor cells by using antibodies against platelet alpha IIb beta 3. However, alpha IIb beta 3 was considered to be expressed strictly in megakaryocyte lineage cells. In order to resolve this controversy, the alpha IIb beta 3-like integrin in murine B16 amelanotic melanoma (B16a) cells was characterized at DNA, RNA, and protein levels. The presence of alpha 5, alpha v, alpha IIb, beta 1, and beta 3 genes in B16a cells was confirmed by Southern analysis. mRNAs for all these integrins except alpha v were detectable by Northern blotting. The alpha IIb beta 3 protein was identified by Western blotting using subunit-specific antibodies and by immunoprecipitation using complex-specific antibody. The alpha IIb beta 3 integrin was localized intracellularly by immunocytochemistry. Finally, alpha IIb and beta 3 mRNAs were amplified by reverse transcription-polymerase chain reaction and the identity of alpha IIb was verified by sequencing. Partial DNA and deduced amino acid sequence analysis showed that B16a alpha IIb shares approximately 80% homology with the human alpha IIb and approximately 90% homology with the rat alpha IIb, whereas B16a alpha IIb shares only approximately 26% homology with the human alpha v. These experiments indicate that the alpha IIb beta 3-like protein in B16a cells is the authentic alpha IIb beta 3 and demonstrate, for the first time, that integrin alpha IIb beta 3 is not confined to megakaryocyte lineage cells.

Expression of 120 kilodalton protein and cytotoxicity in Helicobacter pylori

Antral biopsy culture supernatants from 14 subjects with chronic gastritis, known to have IgA antibodies to the 120 kilodalton protein, showed positive recognition of this antigen in western blots against a cytotoxin positive strain of Helicobacter pylori but gave negative reactions with two cytotoxin negative strains. Control immunoblots with culture supernatants from 13 non-responders to the protein were all negative. This indicates a direct association between expression of the 120 kilodalton protein in H pylori strains and cytotoxicity.

Venous air embolism associated with removal of central venous catheter

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Calcium channel blocker treatment of tumor cells induces alterations in the cytoskeleton, mobility of the integrin alpha IIb beta 3 and tumor-cell-induced platelet aggregation

Calcium channel blockers of the phenylalkylamine (i.e. verapamil), benzothiazepine (i.e. diltiazem) and dihydropyridine (i.e. nifedipine) classes were evaluated for effects on the tumor cell/platelet interactions using Walker 256 carcinosarcoma cells (W256 cells). When W256 cells were pretreated for 15 min with channel blockers at concentrations of 50-200 microM, macroscopic tumor-cell-induced platelet aggregation was inhibited (order of potency; nifedipine greater than diltiazem much greater than verapamil). However, ultrastructural analysis revealed limited, focal platelet aggregates associated with tumor cell plasma membranes of verapamil- and diltiazem-treated cells. There was no evidence of platelet activation or platelet association with the tumor cell membrane in cells pretreated with nifedipine. Walker 256 cells possess the intergrin alpha IIb beta 3. Tumor cell alpha IIb beta 3 was shown to mediate tumor cell/platelet interactions in vitro [Chopra et al. (1988) Cancer Res. 48:3787]. Patching and capping of surface alpha IIb beta 3 were inhibited by nifedipine greater than diltiazem much greater than verapamil. The degree of inhibition of alpha IIb beta 3 receptor mobility parallels the inhibition of tumor-cell-induced platelet aggregation. W256 cells are characterized by a well-developed microfilament and intermediate filament network and by the absence of a distinct microtubular network. Calcium channel blockers had no effect on the low polymerization level of tubulin. However, they induced rearrangement of microfilament stress fibers. Intermediate filaments were also rearranged but to varying degrees. The order of effectiveness for alteration of intermediate filament organization was nifedipine greater than diltiazem while verapamil was ineffective. We propose that the previously reported inhibition of tumor cell/platelet interaction and tumor cell metastasis by calcium channel blockers [Honn et al. (1984) Clin Exp Metastasis 1:61] is due not only to the effects of the Ca2+ channel blockers on platelets, but also to their effect on the tumor cell cytoskeleton resulting in an inhibition of the mobility and function of the alpha IIb beta 3 receptor.

Suspected botulism in three intensively managed Australian cattle herds

Serious outbreaks of a paralytic disease in cattle occurring in the spring and summer of 1988 were investigated on three farms in south eastern Queensland, Australia. On one farm 237 (31 per cent) of 770 cattle died, on the second 109 (40 per cent) of 271 cattle died and on the third 30 (8 per cent) of 380 cows died. Botulism was suspected on the basis of the clinical signs, the lack of significant pathology, a failure to incriminate other agents and a positive feeding trial in one sheep. Laboratory tests for the presence of botulinum toxin failed to confirm this diagnosis, and further feeding trials using ingredients of two rations were also negative.

Is there a role for the tumor cell integrin alpha IIb beta 3 and cytoskeleton in tumor cell-platelet interaction?

In vitro tumor cell-platelet interaction was examined using B16 amelanotic (B16a) melanoma cells. These tumor cells express the alpha IIb beta 3-type cytoadhesin. Aggregation studies demonstrated that tumor cell surface alpha IIb beta 3 mediates the recognition of platelets since pretreatment of tumor cells with antibody against alpha IIb beta 3 prevents platelet-tumor cell interaction as well as platelet activation measured by aggregometry, platelet eicosanoid metabolism and ultrastructural analysis. In B16a cells, disruption of the microfilaments and intermediate filaments inhibits mobility of alpha IIb beta 3 on the cell surface. Microtubules do not play a role in receptor mobility, because B16a cells do not possess well-defined microtubules in interphase and colchicine does not affect receptor mobility. Disruption of microfilaments or intermediate filaments results in an inhibition of tumor cell-platelet interaction as evidenced by aggregometry studies and ultrastructural analysis. We suggest that platelet interaction with tumor cells begins with alpha IIb beta 3-mediated receptor recognition followed by not only platelet activation but also microfilament- and vimentin intermediate filament-dependent tumor cell activation.

Does the introduction of a new player, the endoplasmic reticulum, create more or less confusion in understanding the mechanism(s) of pigmentary organelle translocations?

In 1925, Wilson listed, in his classic third edition of Cell in Development and Heredity, four theories for the morphological and physiological characteristics of cytoplasm; each theory provided some sort of explanation as to the mechanism(s) of organelle translocations. During the past twenty years, cell biologists have focused their attentions on the cell's cytoskeleton, microtrabecular lattice, and associated mechanochemical motors which drive organelles along cytoskeletal tracks. A number of cell types have been used to study organelle translocations, but chromatophores, pigment cells, from cold-blooded vertebrates have been one of the more popular models. This article reviews some of the research findings during the past twenty years, particularly those involving cytoplasmic elements: i.e, microfilaments, intermediate filaments, microtubules, and mechanochemical motors. In addition, it contrasts the proposed involvement of these elements in organelle translocations with the endoplasmic reticulum, a tubulovesicular organelle, which we recently demonstrated is responsible, through its elongation or retraction, for the translocations of carotenoid droplets in goldfish xanthophores and swordtail fish erythrophores. Here, the carotenoid droplets are not free in the cytoplasm and do not translocate via cytoskeletal tracks, but instead are attached to or are a part of the endoplasmic reticulum. On the other hand, carotenoid droplets of squirrel fish erythrophores are free in the cytoplasm and appear to translocate via microtubules. Finally, the rates of pigmentary organelle translocations are reviewed in light of the participation of the cytoskeletal elements with the endoplasmic reticulum.

The activity of the EcoRV restriction endonuclease is influenced by flanking DNA sequences both inside and outside the DNA-protein complex

The EcoRV restriction endonuclease cleaves DNA not only at its recognition sequence but also at most other sequences that differ from the recognition site by one base pair. Compared to the reaction at the recognition site, the reactions at noncognate sites are slow but 1 out of the 12 noncognate sites on the plasmid pAT153 is cleaved more than 50 times faster than any other. The increase in the reaction rate at the preferred noncognate site, relative to other sites, was caused by the DNA sequences in the 4 base pairs from either side of the site. For enhanced activity by EcoRV, particular bases were needed immediately adjacent to the site, inside the DNA-protein complex. At these loci, the protein interacts with the phosphate groups in the DNA and the flanking sequence may control the activity of the enzyme by determining the conformation of the DNA, thus aligning the phosphate contacts. But the preferential cleavage also depended on sequences further away from the site, at loci outside the complex. At external positions, beyond the reach of the protein, the EcoRV enzyme required flanking sequences that give rise to flexibility in DNA conformation. These may facilitate the distortion of the DNA required for catalysis by EcoRV.