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PubMed2006

Survival of three species of anuran metamorphs exposed to UV-B radiation and the pathogenic fungus Batrachochytrium dendrobatidis.

When exploring the possible factors contributing to population declines, it is necessary to consider multiple, interacting environmental stressors. Here, we investigate the impact of 2 factors, ultraviolet radiation and disease, on the survival of anuran amphibians. Exposure to ultraviolet-B (UV-B) radiation increases mortality and results in various sub-lethal effects for many amphibian species. Infectious diseases can also negatively impact amphibian populations. In this study, we exposed metamorphic individuals (metamorphs) to both UV-B and Batrachochytrium dendrobatidis (BD), a fungal pathogen and cause of the disease chytridiomycosis, and monitored survival for 3 wk. We tested for possible interactions between UV-B and BD in 3 species: the Cascades frog Rana cascadae; the Western toad Bufo boreas; and the Pacific treefrog Hyla regilla. We found strong interspecific differences in susceptibility to BD. For example, R. cascadae suffered a large increase in mortality when exposed to BD; B. boreas also experienced mortality, but this effect was small relative to the R. cascadae response. H. regilla did not show any decrease in survival when exposed to either factor. No synergistic interactions between UV-B and BD were found for any of the test species. A previous study investigating the impact of BD on larval amphibians showed different species responses (Blaustein et al. 2005a). Our results highlight the importance of studying multiple life history stages when determining the impact of environmental stressors. The contrast between these 2 studies emphasizes how vulnerability to a pathogen can vary between life history stages within a single species.

Animals↗

PubMedDate not supplied

[Fluorescent analysis of cryopreserved totipotent cells of amphibian embryos].

The cryotolerance of totipotent cells from dissociated embryos of amphibian (grass frog Rana temporaria and grey toad Bufo bufo) was studied. Cell integrity and preservation of the cell barrier function were evaluated by fluorescent analysis. It was shown that the best cryopreservation of the cells was achieved by using the cryoprotective agent 10% dimethyl sulfoxide and 10% saccharose. These cells were successfully used for the homotransplantation of nuclei into enucleated eggs. The development of reconstructed eggs to the blastula stage was noted.

Animals↗

PubMedDate not supplied

[Changes in the permeability of amphibian embryo envelope for fluorochromes under the action of ultrasound].

It was determined whether high-frequency ultra sound can change the permeability of gray toad Bufo bufo and grass frog Rana temporaria under the action of high-frequency ultrasound. The changes in the permeability of embryonic envelope were assessed by using slowly penetrating fluorochromes ANS, FDA, and fluorescein. It was found that the ultrasound of 0.88 MHz and 0.4 - 0.7 W/cm2 intensity increased the permeability of amphibian embryonic envelope for ANS and FDA, whereas the ultrasound of 2.64 MHz and the same intensity increased that for fluorescein with the retention of low permeability for FDA. Embryos continued the normal development after treatment with ultrasound under these conditions.

Animals↗

PubMed1984

Tubular myelin structures in the lungs of amphibia. The mode of formation.

The lungs of the tree frog Hyla arborea and the toad Bufo bufo were fixed in glutaraldehyde with the addition of picric acid or tannic acid to visualize tubular myelin (TM), one of the forms of pulmonary surfactant. The lungs of both Hyla and Bufo are complex in structure and possess one type of pneumocytes containing numerous lamellar bodies (LBs). The alveolar lining layer in the lung of Hyla includes numerous LBs at different stages of transformation into a monolayer film, but the lattice is sparse, delicate and unstable. The structure of smooth membranes in the alveolar layer is not clearly visible and their thickness varies from 4.0 to 7.2 nm. In the lung of Bufo TM occurs commonly in the alveolar lining layer. Membranes of LBs are smooth particle-free bilayers of 8.1 to 12.0 nm thick. During transformation into TM, the membranes become covered by fuzzy coat and irregularly spaced rod-like particles of 8 to 13 nm in diameter. I suppose that these particles facilitate the maintenance of TM structures.

Animals↗

PubMed1997

Spinal ascending pathways in amphibians: cells of origin and main targets.

As part of a research program on the evolution of somatosensory systems in vertebrates, the various components of ascending spinal projections were studied with in vivo and in vitro tract-tracing techniques in representative species of amphibians (the large green frog, Rana perezi, the clawed toad, Xenopus laevis and the ribbed newt, Pleurodeles waltl). Three main ascending sensory channels, each with largely separate targets, were demonstrated: 1. Ascending projections via the dorsal funiculus include primary and nonprimary projections that ascend to terminate mainly in the dorsal column nucleus at obex levels. A small component ascends farther rostralwards to terminate in the reticular formation, the octavolateral area, the trigeminal nuclear complex, and in the granular layer of the cerebellum. 2. Projections ascending via the dorsolateral funiculus reach other spinal and supraspinal targets than the dorsal funicular fibers, mainly ipsilaterally. At upper cervical cord and obex levels, many fibers innervate a region considered the amphibian homologue of the lateral cervical nucleus of mammals. In the medulla, these fibers ascend ventral to the descending trigeminal tract to terminate in the dorsal column and the solitary tract nuclei, and more rostrally, in the reticular formation, the descending trigeminal nucleus and the medial aspect of the ventral octaval nucleus. Major projections reach the area between the facial motor nucleus and the ventral octaval nucleus, and a mediolateral subcerebellar band. These projections arise in neurons located mainly in the ipsilateral deep dorsal and lateral fields throughout the spinal cord. 3. Ascending spinal projections via the ventral quadrant of the spinal cord (the ventral and ventrolateral funiculi) ascend throughout the brainstem up to the diencephalon. Along its course, this component innervates various parts of the reticular formation, the octavolateral area, the granular layer of the cerebellum, the region ventromedial and ventrolateral to the isthmic nucleus, and the subcerebellar region. In the mesencephalon, the torus semicircularis, the midbrain tegmentum and, sparsely, the tectum mesencephali are innervated. Beyond the midbrain, various dorsal and particularly ventral thalamic nuclei and the posterior tubercle are innervated by this ascending sensory channel. The cells of origin of some of these projections were observed in the dorsal, and to a lesser extent, in the lateral and ventral spinal fields of the spinal cord. Evidence for the presence of these three main ascending sensory channels throughout vertebrates will be discussed. The presence of such channels appears to be a shared character in the brain of both amniotes and anamniotes.

Afferent Pathways↗

PubMed1995

Changes in motoneuron membrane potential and reflex activity induced by sudden cooling of isolated spinal cords: differences among cold-sensitive, cold-resistant and freeze-tolerant amphibian species.

The effects of sudden cooling of the spinal cord were studied in three species of amphibians--a cold-sensitive tropical toad (Bufo marinus), a cold-resistant, aquatic, hibernating frog (Rana pipiens, northern leopard frog) and a freeze-tolerant frog (Rana sylvatica, wood frog). Ventral root (motoneuron) potentials were recorded from isolated, hemisected spinal cords of each species mounted in a sucrose-gap recording apparatus and superfused with HCO3(-)-buffered Ringer's solution at room temperature (21 degrees C). In the toad, sudden cooling to 6-8 degrees C produced large, sustained motoneuron depolarizations that returned slowly to baseline levels and were accompanied by extensive paroxysmal activity. Larger, but shorter-lasting, motoneuron depolarizations associated with only a limited amount of paroxysmal activity were generated by rapid cooling of the leopard frog spinal cord. Small, brief motoneuron depolarizations followed by a hyperpolarization, or hyperpolarizations not preceded by depolarizations, were seen in cooled wood frog spinal cords. The wood frog displayed a large amount of spontaneous motoneuron activity, but little paroxysmal activity in response to sudden cooling. Following prolonged cooling, rewarming the spinal cords of all three species resulted in motoneuron hyperpolarizations that slowly decayed towards the baseline value. The amplitude of the rewarming-induced response was larger and longer in toad motoneurons than in leopard frog and wood frog motoneurons. At room temperature, a single supramaximal dorsal root stimulus evoked a depolarizing ventral root potential in toad and leopard frog motoneurons that was decreased in amplitude and prolonged when the spinal cords were cooled to 8 degrees C or below. In contrast, at room temperature, the ventral root reflex in the wood frog was followed by a distinct hyperpolarization. Cooling the wood frog spinal cord only slightly reduced the amplitude of the ventral root potential. In contrast, the evoked hyperpolarization was blocked by sudden cooling and also by the addition of dihydro-ouabain to the Ringer's solution. The motoneuron hyperpolarizations induced by sudden cooling in the wood frog were converted to depolarizations when Cl- in the superfusate was replaced with isethionate. The depolarizations elicited by sudden cooling were reduced by the addition of kynurenate in all three species. A dose-response curve generated by short applications of L-glutamate demonstrated that wood frog motoneurons were less sensitive than leopard frog motoneurons to L-glutamate. In summary, three species of amphibians, differing in their adaptations to the temperature of their environments, vary in their responses to sudden reductions in temperature. The relationship of these responses to their environmental adaptations remains to be determined.

Animals↗

PubMed2005

Electrophoretic and functional identification of two troponin C isoforms in toad skeletal muscle fibers.

The differential sensitivity of frog twitch and slow-tonic fibers to Ca(2+) and Sr(2+) suggests that these two fiber types express different troponin C (TnC) isoforms. To date, only one TnC isoform from anurans (resembling the mammalian fast-twitch isoform) has been isolated and characterized. In this study, we examined the possibility that anuran striated muscle contains more than one TnC isoform. Toward this end, we determined the TnC isoform composition of 198 single fibers from the rectus abdominis of the cane toad (a mixed slow-tonic and twitch muscle) and of toad cardiac muscle using a method that enables the identification of TnC isoforms on the basis of the effect of Ca(2+) on their electrophoretic mobility. The fibers were typed according to their myosin heavy chain (MHC) isoform composition. The data indicate that striated muscle of the cane toad contains two TnC isoforms, one of which (TnC-t) is present in all fibers displaying only twitch MHC isoforms and the other of which (TnC-T/c) is present in fibers displaying the tonic MHC isoform and in cardiac muscle. For a subpopulation of 15 fibers, the TnC isoform composition was also compared with Ca(2+) and Sr(2+) activation characteristics. Fibers containing the TnC-T/c isoform were approximately 3-fold more sensitive to Ca(2+), approximately 40-fold more sensitive to Sr(2+), and responded to a approximately 4.6-fold broader range of [Ca(2+)] than did fibers containing the TnC-t isoform. The Ca(2+) activation properties of toad fibers containing the TnC-T/c isoform appear to be consistent with the previously reported physiological characteristics of amphibian slow-tonic muscle fibers.

Animals↗

PubMed1984

Current-voltage relations of the basolateral membrane in tight amphibian epithelia: use of nystatin to depolarize the apical membrane.

Exposure of the mucosal side of toad (Bufo bufo) urinary bladder and frog (Rana ridibunda) skin to the polyene ionophore nystatin, resulted in stable preparations in which the apical resistance was negligible compared to the basolateral resistance. The preparations support passive K currents in both directions and an amiloride-insensitive Na current in the apical-serosal direction which is blocked by ouabain. The nystatin-treated toad bladder was used to study the electrical properties of the basolateral membrane by means of current-voltage curves recorded transepithelially. The K current showed strong rectification at cellular potentials negative with respect to the interstitial space. The ouabain-sensitive current increased with membrane voltage at negative voltages but saturated above +20 mV.

Animals↗

PubMed2005

Metamorphosis of two amphibian species after chronic cadmium exposure in outdoor aquatic mesocosms.

Amphibian larvae at contaminated sites may experience an alteration of metamorphic traits and survival compared to amphibians in uncontaminated conditions. Effects of chronic cadmium (Cd) exposure on the metamorphosis of American toads (Bufo americanus) and southern leopard frogs (Rana sphenocephala) were determined. The two species were reared separately from shortly after hatching through metamorphosis in outdoor mesocosms (1,325-L polyethylene cattle tanks) that simulated natural ponds and enhanced environmental realism relative to the laboratory. Both species exhibited a decrease in survival with increasing initial nominal aqueous Cd concentration. Cadmium treatment did not influence mass at metamorphosis for either species when survival was included as a covariate, but increased the age at metamorphosis for the American toads. The whole body Cd content of metamorphs increased with aqueous Cd treatment level for both species, and the American toads tended to possess more elevated residues. Cadmium quickly partitioned out of the water column and accumulated in and altered the abundance of the tadpoles' diet. Cadmium-contaminated sites may produce fewer metamorphs, and those that survive will metamorphose later and contain Cd. Interspecific differences in the response variables illustrate the importance of testing multiple species when assessing risk.

Animals↗

PubMed1978

Effect of amiloride on chloride transport across amphibian epithelia.

Amiloride is found to inhibit chloride exchange diffusion in toad skin and passive chloride transport in frog skin. In both tissues, chloride transport is reactivated by substituting with KCl-Ringer's on the inside, so the effect of amiloride on chloride transport is secondary to its well-known inhibition of sodium transport. Removal of chloride from the outside bathing solution inhibits chloride outflux in both tissues. This is easy to explain in the case of the toad skin where chloride transport under short-circuit conditions occurs as exchange diffusion. In the frog skin this transeffect indicates that the chloride concentration at a location very near the outer surface is of significance for chloride permeability. The possibility is discussed that the chloride concentration in the outward facing membrane, or in compartments near to it, regulates chloride fluxes across frog skin.

Amiloride↗

PubMed1994

Urea and salt effects on enzymes from estivating and non-estivating amphibians.

The effects of urea, cations (K+,NH4,Na+,Cs+,Li+), and trimethylamines on the maximal activities and kinetic properties of pyruvate kinase (PK) and phosphofructokinase (PFK) from skeletal muscle were analyzed in two anuran amphibians, an estivating species, the spadefoot toad Scaphiopus couchii, and a semi-aquatic species, the leopard frog Rana pipiens. Urea, which accumulates naturally to levels of 200-300 mM during estivation in toads, had only minor effects on the Vmax, kinetic constants and pH curves of PK from either species and no effects on PFK Vmax or kinetic constants. Trimethylamine oxide neither affected enzyme activity directly or changed enzyme response to urea. By contrast, high KCl (200 mM) lowered the Vmax of toad PFK and of PK from both species and altered the Km values for both substrates of frog PFK. Other cations were even more inhibitory; for example, the Vmax of PK from either species was reduced by more than 80% by the addition of 200 mM NH4Cl, NaCl, CsCi, or LiCl. High KCl also significantly changed the Km values for substrates of toad lactate dehydrogenase and strongly reduced the Vmax of glutamate dehydrogenase and NAD-dependent isocitrate dehydrogenase in both species whereas 300 mM urea had relatively little effect on these enzymes. The perturbing effect of urea on enzymes and the counteracting effect of trimethylamines that has been reported for elasmobranch fishes (that maintain high concentrations of both solutes naturally) does not appear to apply to amphibian enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2001

Descending supraspinal pathways in amphibians. I. A dextran amine tracing study of their cells of origin.

The present study is the first of a series on descending supraspinal pathways in amphibians in which hodologic and developmental aspects are studied. Representative species of anurans (the green frog, Rana perezi, and the clawed toad, Xenopus laevis), urodeles (the Iberian ribbed newt, Pleurodeles waltl), and gymnophionans (the Mexican caecilian, Dermophis mexicanus) have been used. By means of retrograde tracing with dextran amines, previous data in anurans were largely confirmed and extended, but the studies in P. waltl and D. mexicanus present the first detailed data on descending pathways to the spinal cord in urodeles and gymnophionans. In all three orders, extensive brainstem-spinal pathways were present with only minor representation of spinal projections originating in forebrain regions. In the rhombencephalon, spinal projections arise from the reticular formation, several parts of the octavolateral area, the locus coeruleus, the laterodorsal tegmental nucleus, the raphe nucleus, sensory nuclei (trigeminal sensory nuclei and the dorsal column nucleus), and the nucleus of the solitary tract. In all species studied, the cerebellar nucleus and scattered cerebellar cells innervate the spinal cord, predominantly contralaterally. Mesencephalic projections include modest tectospinal projections, torospinal projections, and extensive tegmentospinal projections. The tegmentospinal projections include projections from the nucleus of Edinger-Westphal, the red nucleus, and from anterodorsal, anteroventral, and posteroventral tegmental nuclei. In the forebrain, diencephalospinal projections originate in the ventral thalamus, posterior tubercle, the pretectal region, and the interstitial nucleus of the fasciculus longitudinalis medialis. The most rostrally located cells of origin of descending spinal pathways were found in the suprachiasmatic nucleus, the preoptic area and a subpallial region in the caudal telencephalic hemisphere, probably belonging to the amygdaloid complex. Our data are discussed in an evolutionary perspective.

Amphibians↗

PubMed2001

Descending supraspinal pathways in amphibians. II. Distribution and origin of the catecholaminergic innervation of the spinal cord.

Immunohistochemical studies with antibodies against tyrosine hydroxylase, dopamine, and noradrenaline have revealed that the spinal cord of anuran, urodele, and gymnophionan (apodan) amphibians is abundantly innervated by catecholaminergic (CA) fibers and terminals. Because intraspinal cells occur in all three orders of amphibians CA, it is unclear to what extent the CA innervation of the spinal cord is of supraspinal origin. In a previous study, we showed that many cell groups throughout the forebrain and brainstem project to the spinal cord of two anurans (the green frog, Rana perezi, and the clawed toad, Xenopus laevis), a urodele (the Iberian ribbed newt, Pleurodeles waltl), and a gymnophionan (the Mexican caecilian, Dermophis mexicanus). To determine the exact site of origin of the supraspinal CA innervation of the amphibian spinal cord, retrograde tracing techniques were combined with immunohistochemistry for tyrosine hydroxylase in the same sections. The double-labeling experiments demonstrated that four brain centers provide CA innervation to the amphibian spinal cord: 1.) the ventrolateral component of the posterior tubercle in the mammillary region, 2.) the periventricular nucleus of the zona incerta in the ventral thalamus, 3.) the locus coeruleus, and 4.) the nucleus of the solitary tract. This pattern holds for all three orders of amphibians, except for the CA projection from the nucleus of the solitary tract in gymnophionans. There are differences in the strength of the projections (based on the number of double-labeled cells), but in general, spinal functions in amphibians are controlled by CA innervation from brain centers that can easily be compared with their counterparts in amniotes. The organization of the CA input to the spinal cord of amphibians is largely similar to that described for mammals. Nevertheless, by using a segmental approach of the CNS, a remarkable difference was observed with respect to the diencephalic CA projections.

Amphibians↗

PubMed1995

Anuran dorsal column nucleus: organization, immunohistochemical characterization, and fiber connections in Rana perezi and Xenopus laevis.

As part of a research program on the evolution of somatosensory systems in vertebrates, the dorsal column nucleus (DCN) was studied with (immuno)histochemical and tract-tracing techniques in anurans (the large green frog, Rana perezi, and the clawed toad, Xenopus laevis). The anuran DCN contains some nicotinamide adenine dinucleotide phosphate diaphorase-positive neurons, very little calbindin D-28k, and a distinct parvalbumin-positive cell population. The anuran DCN is innervated by primary and non-primary spinal afferents, by primary afferents from cranial nerves V, VII, IX, and X, by serotonin-immunoreactive fibers, and by peptidergic fibers. Non-primary DCN afferents from the spinal cord appear to arise throughout the spinal cord, but particularly from the ipsilateral dorsal gray. The present study focused on the efferent connections of the DCN, in particular the targets of the medial lemniscus. The medial lemniscus could be traced throughout the brainstem and into the diencephalon. Along its course, the medial lemniscus gives off collaterals to various parts of the reticular formation, to the octavolateral area, and to the granular layer of the cerebellum. At mesencephalic levels, the medial lemniscus innervates the lateral part of the torus semicircularis as well as various tegmental nuclei. A striking difference between the two species studied is that while in R. perezi medial lemniscal fibers do not reach the tectum mesencephali, in X. laevis, intermediate and deep tectal layers are innervated. Beyond the midbrain, both dorsal and ventral thalamic areas are innervated by the medial lemniscus. The present study shows that the anuran "lemniscal pathway" is basically similar to that of amniotes.

Animals↗

PubMed1995

Factors influencing testosterone metabolism by anuran larvae.

The effects of experimental conditions--steroid concentration, temperature, treatment duration, tadpole density, and delivery mode--on testosterone (T) metabolic rates were examined in larval anurans. T uptake into tadpoles was measured by scintillation counting of [3H]T and metabolism of T was studied by thin layer chromatography in two anuran species, the African clawed frog (Xenopus laevis) and the western toad (Bufo boreas). T was extensively metabolized by both species, but the effects of each experimental condition on T metabolism varied between species. In the study of delivery mode, tadpoles injected with T dissolved in saline metabolized T faster than animals in groups where the steroid was added directly to the water. Animals injected with T dissolved in oil metabolized T the slowest, but T was short-lived in all cases. The current study demonstrates that concentration, temperature, treatment duration, tadpole density, and delivery mode may all affect steroid metabolic rates, but these effects vary between species in unpredictable ways. Since steroid metabolism may either activate or deactivate steroids, these factors are important in understanding the potency of steroids in tadpoles. A review of the literature dealing with steroid effects in anuran larvae illustrates these problems.

Analysis of Variance↗

PubMed2001

PCBs and their putative effects on polecat (Mustela putorius) populations in Central Europe.

In Europe polecat populations are declining for unknown reasons during the last decades. Data on the river otter, another mustelid predator, indicate that PCB levels are high enough in some populations to interfere with the reproduction of this aquatic species. Since the diet of the polecats consists to a large amount of aquatic prey (amphibians) it appears reasonable to assume that PCBs ingested with the prey are a factor in the decline of polecats. To test this assumption PCB residues in amphibians and in adipose tissue and liver of polecats from Southwest Germany were quantified and the results were compared with literature data on the reproductive toxicity of PCBs in feral mink. According to the current data total PCB levels in polecats (adipose tissue, mean 1244 ng/g lipids; liver, mean 1677 ng/g lipids) and their prey (frogs, mean 9279 ng/kg fresh weight; toads, 4948 ng/kg fresh weight) are comparatively low. Using the toxic equivalent approach, it was calculated that polecats could feed exclusively on amphibians without consuming a harmful amount of PCBs. Therefore, PCBs cannot be an agent currently affecting polecat populations in Central Europe. Other environmental factors like habitat destruction or road accidents are more likely to have a negative impact on polecat populations.

Adipose Tissue↗

PubMed1987

A comparison of energy substrates and reproductive patterns of two anurans. Acris crepitans and Bufo woodhousei.

The seasonal pattern of carcass, liver and ovary lipid and liver non-lipid mass was examined in the cricket frog, Acris crepitans, and Woodhouse's toad, Bufo woodhousei. Reproductive patterns were also studied. The over-winter reduction of body lipid and liver non-lipid material was attributed to metabolism in Acris crepitans. Male, but not female, Bufo woodhousei exhibited seasonal variation in lipid stores that was attributable to metabolism. Females, but not males, showed seasonal variation in liver non-lipid mass and quantified liver glycogen. Females of both species mobilized body lipid during the period of ovarian development; however, an inverse relationship between fatbody mass and ovary mass was evident for Acris, only. Female Acris crepitans depleted all ovarian follicles prior to brumation; however, Bufo woodhousei retained enlarged follicles throughout the year. Variation in metabolic substrate use between species was related to the differences in reproductive patterns exhibited by the two anurans. These variations in reproductive strategy represent adaptations that enhance the survivability of different species in dissimilar habitats.

Acclimatization↗

PubMed1992

Comparison of the sequence and structure of transcription factor IIIA from Bufo americanus and Rana pipiens.

Amino acid (aa) sequences of transcription factor IIIA (TFIIIA) from the toad, Bufo americanus, and the grass frog, Rana pipiens, were determined by cDNA cloning and DNA sequencing. The 3'-untranslated regions of the cDNAs reveal that the TFIIIA gene polyadenylation signal is ATTAAA, rather than the conventional AATAAA. The B. americanus and R. pipiens proteins share about 60% aa sequence homology with each other and with Xenopus laevis TFIIIA. Although these results indicate that TFIIIA has more sequence variation than other DNA-binding proteins, a number of conserved features are evident and of likely functional significance. These include potential guanine nucleotide-binding sites at arginines in zinc fingers (ZnF) II, V, and IX, acidic residues between metal-coordinating cysteines, and a basic region in the C-terminal tail possibly involved in transcription promotion. Sequence similarity also exists in an aa stretch bridging the ninth ZnF and C-terminal tail of both TFIIIA and the 5S RNA-binding protein, p43. DNase I protection analyses demonstrate that B. americanus and R. pipiens TFIIIA interact with the internal control region (ICR) of the Xenopus borealis 5S RNA-encoding gene (5S) in different manners: the B. americanus interaction is similar to X. laevis TFIIIA, protecting the entire 5S gene ICR (nt +96 to +43) from DNase I digestion, whereas the R. pipiens TFIIIA strongly protects the ICR from nt +96 up to +78 and less strongly from +78 to +43. Possibly accounting for the binding differences observed, R. pipiens and R. catesbeiana oocyte 5S RNAs (and by inference 5S genes) were found to contain a G or U at nt position 50 while B. americanus, X. laevis, and other eukaryotic 5S RNAs have an A in the analogous position (nt 53 in generalized eukaryotic structure).

Amino Acid Sequence↗