Entry Phase Research Articles

Electromyographic Analysis of the Backstroke Start with Different Feet Positions

To the best of our knowledge, no study has yet analyzed the most effective backstroke start variant based on the most recent rules modification endorsed by the Federation Internationale de Natation particularly regarding the neuro-muscular activation involved in the force production and stabilization of the body. PURPOSE: To analyze the electromyographic (EMG) activity of the propulsive and stabilizing muscles during backstroke starts performed with the feet submerged (BSFI) and with the feet above the water surface (BSFE). METHODS: Four high-level male swimmers (22.8±1.7 years, 75.9±8.9 kg, 1.78±0.06 m and 15.5±5.0 years of training experience) performed two sets of six maximal repetitions using BSFI and BSFE over a distance of 15m. Surface EMG signals of Deltoideus Anterior, Biceps Brachii, Triceps Brachii, Erector Spinae Longissimus, Gluteus Maximus, Rectus Femoris and Gastrocnemius Medialis were obtained. A qualitative video analysis was used to breakdown the backstroke start into five phases: hands-off, take-off, flight, entry and glide. The raw EMG signals were rectified, smoothed (10Hz), then integrated (IEMG) and normalized to maximum voluntary contractions and time. Descriptive statistics and paired Student's t test were used (p<0.05). RESULTS: During the hands-off phase it was registered higher IEMG for the Biceps Brachii and Erector Spinae Longissimus at BSFE comparing with BSFI (8.26±2.63% vs 3.85±1.37%, p<0.001; 3.85±1.27% vs 1.28±0.81%, p<0.001, respectively). No differences between start variants were observed in the take-off phase. For the 3rd phase (flight), BSFE presented higher IEMG on Deltoideus Anterior (1.63±0.78% vs 0.99±0.37%, p=0.01), Biceps Brachii (1.28±0.78% vs 0.93±0.78%, p<0.01), and Erector Spinae Longissimus (1.47±0.54 vs 0.63±0.56%, p<0.001). During the entry phase, the value of Erector Spinae Longissimus was lower for BSFI than for BSFE (2.11±1.85% vs 4.20±2.21%, p<0.001). The IEMG value for Biceps Brachii and Erector Spinae Longissimus at last phase (the glide) was higher for BSFE (1.28±0.31% vs 0.98±0.18%, p<0.01; 3.27±1.20 vs 1.97±1.43, p=0.01, respectively). CONCLUSIONS: The BSFE seems to require higher myoelectric activation than the BSFI from the stabilizing muscles of the back and the arms during the initial and middle part of the start movement.

Characteristics of 150 km echoes linked with solar eclipse and their implications to the echoing phenomenon

[1] This paper presents a study based on Gadanki radar observations of 150 km echoes made during the solar eclipse of 15 January 2010 that occurred during 1122–1515 IST. Radar echoes were observed only during 1150–1215 IST and 1344–1356 IST linked with the entry and recovery phases of the eclipse, respectively. The most striking observation found is the unusual ascending and descending features of the echoing regions observed during these two time periods. Although these echoes occurred at higher altitudes than those of control days, SNR and spectral width of these echoes are similar to those of the lower echoing region observed on the control days. Further, Doppler velocities suggest the presence of westward electric field unlike those of the control days. Concurrent ionosonde observations showed ascent and descent of the F1 layer very similar to those observed in the 150 km echoes. These observations and related analysis suggest that the observed echoes were due to the combined action of the electron density gradients and the reduced recombination rate linked with the solar eclipse effect. These observations are first of its kind and elucidate the role of density gradient and recombination rate in the 150 km echoing process.

The Role of Guidance Counsellors in Universal Basic Education School Based Assessment

This monograph on the role of guidance counsellors in School Based Assessment of Universal Basic Education explored the counselling features of the 6:3:3:4 curriculum such as multiple entry and exit phases, monitoring, functionalism and continuous assessment. It also explored the origin of the school based assessment; the difference between it and the current concept of continuous assessment and the functions of counsellors in the implementation of the school based assessment. The weaknesses of the previous UPE which failed to achieve its objective were highlighted to promote precautionary measures. The paper ended with recommendations on the necessary changes the government and counsellors can make to neutralize the impression that counselling is the same as advice giving and to realize the counselling objectives of the Universal Basic Education. Key Words: Education, Counsellors, Assessment, Nigeria

Influence of Falling Height on the Behavior of Skid- Launching Free-Fall Lifeboat in Regular Waves

This paper numerically investigated the influence of falling height on the behavior of the skid-launching free-fall lifeboat (FFLB) in regular waves. The boat has been treated as a rigid body when the differential equations of motion for the four falling phases, i.e., sliding or ramp phase, rotation phase, free-fall phase and water entry phase of the lifeboat were solved in the time domain. The hydrodynamic characteristics of the lifeboat has been studied for different falling heights such as H = 1.5m, 1.75m and 2.00m. Horizontal and vertical excursions and the rotation of the axis of the boat have been computed at different time along with its horizontal and vertical velocities. Hydrodynamic forces and accelerations at normal and axial directions have also been determined. At first the analysis has been done in still water and then in regular wave with amplitude of 0.5m and a period of 2.0 sec. In all of the cases, effects of regular wave are shown by comparing the results with those considering the falling of FFLB into calm water.

Comparison of Grab Start between Elite and Trained Swimmers

This study analysed motor control during front crawl swimming starts by elite and trained swimmers, based on comparisons of: 1) kinematic and kinetic parameters of the start and 2) variability of these parameters across 3 trials per swimmer. Given that the start time to the 15-m mark is greatly influenced by the swimming phase, the study also compared the stroking and coordinative parameters from water entry to 25-m in the 2 skill groups. The swimmers performed 3 x 25-m at the 50-m race-pace and used their preferential start technique (grab start). The elite swimmers showed better start organization as reflected by higher impulse values in the direction of intended displacement despite similar block phase durations. They then spent more time in the water entry, gliding and leg kicking phases, with shorter swimming phase duration and 15-m start time than the trained swimmers (p<0.05). The trained swimmers showed significantly lower values for stroke length and velocity (p<0.05) during the swimming phase. Analysis revealed low intra-subject variability (across the 3 trials) but high inter-subject variability, indicating that both elite and trained swimmers had mastered distinct, though different, motor patterns.

Arm coordination, power, and swim efficiency in national and regional front crawl swimmers

The effects of skill level on index of arm coordination (IdC), mechanical power output ( P d), and swim efficiency were studied in front crawlers swimming at different speeds. Seven national and seven regional swimmers performed an arms-only intermittent graded speed test on the MAD-system and in a free condition. The MAD-system measured the drag ( D) and P d. Swimming speed ( v), stroke rate (SR), stroke length (SL), stroke index (SI), relative entry, pull, push, and recovery phase durations, and IdC were calculated. Swim efficiency was assessed from SI, the coefficient of variation of calculated hip intra-cyclic velocity variations ( IVV), and the efficiency of propulsion generation, i.e., the ratio of v 2 to tangential hand speed squared ( u 2). Both groups increased propulsive continuity (IdC) and hand speed ( u) and applied greater P d to overcome active drag with speed increases ( p < .05). This motor organization adaptation was adequate because SI, IVV, and v 2/ u 2 were unchanged. National swimmers appeared more efficient, with greater propulsive continuity (IdC) and P d to reach higher v than regional swimmers ( p < .05). The regional swimmers exhibited a higher u and lower SI, IVV, and v 2/ u 2 compared to national swimmers ( p < .05), which revealed lower effectiveness to generate propulsion, suggesting that technique is a major determinant of swimming performance.

MCAV/IMU integrated navigation for the powered descent phase of Mars EDL

Pin-point landing is considered as a key technology for future manned Mars landing and Mars base missions. The traditional inertial navigation system (INS) based guidance, navigation and control (GNC) mode used in the Mars entry, descent and landing (EDL) phase has no ability to achieve the precise and safe Mars landing, so novel EDL GNC methodologies should be investigated to meet this goal. This paper proposes the MCAV/IMU integrated navigation scheme for the powered descent phase of Mars EDL. The Miniature Coherent Altimeter and Velocimeter (MCAV) is adopted to correct the inertial bias and drift and improve the performance of integrated navigation. Altitude and velocity information derived from MCAV and the lander’s state information sensed by inertial measurement unit (IMU) are integrated in extended Kalman filter algorithm. The validity of the proposed navigation scheme is confirmed by computer simulation.

Global vulnerability to near-Earth object impact

A clear appreciation of the consequences resulting from an asteroid impact is required in order to understand the near-Earth object (NEO) hazard. Three main processes require modelling to analyse the entire impact event. These are the atmospheric entry phase, land impact events and ocean impact events. A range of impact generated effects (IGEs) are produced by different impact scenarios. It is these IGEs that present the threat to human populations worldwide, and the infrastructure they utilise. A software system for analysing the NEO threat has been developed, entitled NEOimpactor, to examine the social and economic consequences from land and ocean impacts. Existing mathematical models for the three principal impact processes have been integrated into one complete system, which has the capability to model the various effects of a terrestrial asteroid impact and, critically, predict the consequences for the global population and infrastructure. Analysis of multiple impact simulations provides a robust method for the provision of an integrated, global vulnerability assessment of the NEO hazard. The primary graphical outputs from NEOimpactor are in the form of ‘relative consequence’ maps, and these have been designed to be comprehensible to a non-specialist audience. By the use of a series of multiple-impact simulations, the system has identified the five countries most at risk from the impact hazard, as well as indicating the various factors influencing vulnerability.

Kinematical Profiling of the Front Crawl Start

This study analysed the start phases of 15 elite front crawl swimmers, all specialists of sprint events. The first aim was to determine which phases were correlated with the 15-m start time. The features common to the sample of swimmers were then established and individual profiles were clustered. The subjects performed two 25-m trials at the 50-m race-pace using their preferential start technique (grab start). The kinematical analysis assessed the durations of the block, flight, entry, glide, leg kicking and full swimming phases to the 15-m mark. Stroking parameters and the index of arm coordination (IdC) were analysed for the swimming part (10-20 m) of the 25-m. Through the swimming part IdC increased while stroke length and velocity decreased (p<0.05). The relative durations of the aerial (block, flight), entry and underwater phases were correlated with start time. Inter-subject variability was observed, which suggests that various motor solutions were used for the start. Notably, four clusters led to a short 15-m start time: the leg kicking style, mixed "leg kicking/swimming" style, long glide style and short glide style.

Pregnancy Enhances Sustained Ca2+ Bursts and Endothelial Nitric Oxide Synthase Activation in Ovine Uterine Artery Endothelial Cells Through Increased Connexin 43 Function1

Endothelium-mediated vasodilation is specifically enhanced in uterine circulation during pregnancy, and production of nitric oxide (NO) is increased in response to a wide array of agonists. Uterine artery endothelial cells from nonpregnant (NP-UAECs) or pregnant (P-UAECs) ewes maintained in culture still show a pregnancy-enhanced difference in ATP-stimulated endothelial NO synthase (eNOS; official symbol NOS3) activation, even though NOS3 protein, purinergic receptors, and associated cell signaling proteins are expressed at equal levels. We have also shown that the pregnancy-enhanced endothelial cell NO response to ATP requires an enhanced and sustained capacitative entry phase that is likely mediated via canonical transient receptor potential protein/inositol 1,4,5-trisphosphate receptor type 2 interaction. In this study, we now show by simultaneous video imaging of individual Fura-2-loaded cells that the pregnancy-enhanced capacitative entry phase is not continuous and equal in all cells, but is in fact mediated as a series of periodic [Ca(2+)](i) bursts within individual cells. Not only does pregnancy increase the number of bursts over a longer time period in individual cells, but also a greater proportion of cells exhibit this burst activity, and at high cell density this occurs in a synchronous manner. The mediator of cell synchronization is connexin 43 (Cx43) gap junctions because 1) Cx43 is readily detectable by Western blot analysis in UAECs, whereas Cx40 and Cx37 are weakly detected or absent, and 2) pregnancy-specific enhancement of [Ca(2+)](i) bursts by ATP is blocked by inhibitory loop peptides selective to Cx43 ((43,37)GAP27) but not by a scrambled control peptide or (40)GAP27 or (40,37)GAP26 peptides, which are specific to Cx40 or Cx37. The relationship between Ca(2+) bursts and NOS3 activation is further established by the finding that (43,37)GAP27 inhibits ATP-stimulated NOS3 activation but has no effect on cell mitogenesis. We conclude that it is pregnancy-enhanced gap junction communication between cells that underlies pregnancy enhancement of capacitative entry via TRPC3 and, in turn, NOS3 activation. Such improved gap junction function allows greater and more sustained [Ca(2+)](i) responses to agents such as ATP within a single cell, as well as the additional recruitment of greater numbers of cells to the response in a coordinated and synchronous manner to support enhanced NO production.

How early opposed to late internationalizers learn: Experience of others and paradigms of interpretation

Although learning plays a pivotal role in the internationalization context of the firm, studies elaborating aspects of learning of early internationalizers (as opposed to late internationalizers) are largely missing. We address this deficit by examining the process of learning in the entry phase of internationalization. Our empirical results show that learning from direct experience is negatively related to early internationalization, whereas learning from others and learning from paradigms of interpretation have a positive impact on early internationalization. Furthermore, our results suggest that early internationalizers compared to late internationalizers continue to prefer cooperative modes of market penetration and show higher entry-mode stability in the same country.

Resveratrol exhibits a strong cytotoxic activity in cultured cells and has an antiviral action against polyomavirus: potential clinical use

BackgroundResveratrol is a non flavonoid polyphenol compound present in many plants and fruits and, at especially high concentrations, in the grape berries of Vitis vinifera. This compound has a strong bioactivity and its cytoprotective action has been demonstrated, however at high concentrations the drug exhibits also an effective anti-proliferative action. We recently showed its ability to abolish the effects of oxidative stress in cultured cells. In this work we assayed the bioactivity of resveratrol as antiproliferative and antiviral drug in cultured fibroblasts. Studies by other Authors showed that this natural compound inhibits the proliferation of different viruses such as herpes simplex, varicella-zoster and influenza A. The results presented here show an evident toxic activity of the drug at high concentrations, on the other hand at sub-cytotoxic concentrations, resveratrol can effectively inhibit the synthesis of polyomavirus DNA. A possible interpretation is that, due to the damage caused by resveratrol to the plasma membrane, the transfer of the virus from the endoplasmic reticulum to the nucleus, may be hindered thus inhibiting the production of viral DNA.MethodsThe mouse fibroblast line 3T6 and the human tumor line HL60 were used throughout the work. Cell viability and vital cell count were assessed respectively, by the MTT assay and Trypan Blue staining. Cytotoxic properties and evaluation of viral DNA production by agarose gel electrophoresis were performed according to standard protocols.ResultsOur results show a clear dose dependent both cytotoxic and antiviral effect of resveratrol respectively at high and low concentrations. The cytotoxic action is exerted towards a stabilized cell-line (3T6) as well as a tumor-line (HL60). Furthermore the antiviral action is evident after the phase of virion entry, therefore data suggest that the drug acts during the synthesis of the viral progeny DNA.ConclusionResveratrol is cytotoxic and inhibits, in a dose dependent fashion, the synthesis of polyomavirus DNA in the infected cell. Furthermore, this inhibition is observed at non cytotoxic concentrations of the drug. Our data imply that cyto-toxicity may be attributed to the membrane damage caused by the drug and that the transfer of polyomavirus from the endoplasmic reticulum to the cytoplasm may be hindered. In conclusion, the cytotoxic and antiviral properties of resveratrol make it a potential candidate for the clinical control of proliferative as well as viral pathologies.

Increased Serum Magnesium and Calcium and their Regulation During Hibernation in the Indian Common Toad,Duttaphrynus melanostictus(Schneider, 1799)

In the present study we investigate the changes in the level of serum magnesium and calcium ions, and their possible mode of regulation during progression of hibernation of the anuran, Duttaphrynus melanostictus, the Indian Common toad. Though these ions have a profound effect on the thermoregulatory center in the brain of even poikilothermic vertebrates like the Indian Common toad, not much information is available about the system. We attempt to expose the role of these ions in this system. In this animal, serum magnesium and calcium levels are known to be significantly low during the entry phase as well as during the awakening phase from the hibernation period as compared to the deepest phase. We tried to correlate the role of serum magnesium and calcium ions during different phases of this poikilothermic animal.

Cardiac Ion Channels

The analysis of the molecular basis of the inherited cardiac arrhythmias has been the driving force behind the identification of the ion channels that generate the action potential. The genes encoding all the major ion channels have cloned and sequenced. The studies have revealed greater complexity than heretofore imagined. Many ion channels function as part of macromolecular complexes in which many components are assembled at specific sites within the membrane. This review describes the generation of the normal cardiac action potential. The properties of the major ionic currents are the examined in detail. Special emphasis is placed on the functional consequences of arrhythmia-associated ion channel mutations. The review concludes with a glimpse of the directions in which this new electrophysiology may lead. The normal sequence and synchronous contraction of the atria and ventricles require the rapid activation of groups of cardiac cells. An activation mechanism must enable rapid changes in heart rate and also respond to the changes in autonomic tone. The propagating cardiac action potential fulfils these roles. Figure 1 illustrates the 5 phases of the normal action potential: 1. Phase 4, or the resting potential, is stable at ≈−90 mV in normal working myocardial cells. 2. Phase 0 is the phase of rapid depolarization. The membrane potential shifts into positive voltage range. This phase is central to rapid propagation of the cardiac impulse (conduction velocity, θ=1 m/s). 3. Phase 1 is a phase of rapid repolarization. This phase sets the potential for the next phase of the action potential. 4. Phase 2, a plateau phase, is the longest phase. It is unique among excitable cells and marks the phase of calcium entry into the cell. 5. Phase 3 is the phase of rapid repolarization that restores the membrane potential to its resting value.1 Figure 1. Membrane currents that generate the a normal …

Investigation on human adrenocortical cell response to adenovirus and adenoviral vector infection

After systemic administration, adenoviral vectors (AdVs) are sequestered in the liver and adrenal glands. Adenoviral vector transduction has been shown to cause cytopathic effects on human hepatocytes and to induce an inflammatory response, whereas the effect of AdVs on human adrenocortical cells has never been investigated. In this study, human adrenocortical carcinoma cell lines and primary cell cultures were used to assess the effects of wild-type adenovirus (Ad5WT) and E1/E3-deleted AdVs on cell proliferation and steroidogenesis. Ad5WT could efficiently replicate in adrenocortical cells, leading to S phase induction, followed by cell death, whereas high titer AdVs transduction had only mild effects on adrenocortical cell proliferation, with accumulation of cells in G2/M. Both AdVs and Ad5WT induced expression of inflammatory cytokines, such as interleukin-6 and tumor necrosis factor-alpha, but, most importantly, they led to a marked and dose-dependent increase of cortisol and other steroid hormone production and consistently modulated expression of key steroidogenic enzymes and regulators of steroidogenesis. This effect, which was already apparent at 6 h post-infection, probably represented a response to adenoviral entry and/or early phases of infection. The result of this study contribute to the understanding of host response to adenoviral vector administration.

The Role of the Mammalian Copper Transporter 1 in the Cellular Accumulation of Platinum-Based Drugs

The mammalian copper transporter 1 (CTR1) is responsible for the uptake of copper from the extracellular space. In this study, we used an isogenic pair of CTR1(+/+) and CTR1(-/-) mouse embryo fibroblasts to examine the contribution of CTR1 to the influx of cisplatin (DDP), carboplatin (CBDCA), oxaliplatin (L-OHP), and transplatin. Exposure to DDP triggered the rapid degradation of CTR1, suggesting that its contribution to influx was likely to be on the initial phase of drug entry. Loss of CTR1 decreased the initial binding of DDP to cells and reduced influx measured over the first 5 min of drug exposure by 81%. Loss of CTR1 almost completely eliminated the initial influx of CBDCA and reduced the initial uptake of L-OHP by 68% but had no effect on the influx of transplatin. Loss of CTR1 rendered cells resistant to even high concentrations of DDP when measured in vitro, and re-expression of CTR1 in the CTR1(-/-) cells restored both DDP uptake and cytotoxicity. The growth of CTR1(-/-) tumor xenografts in which CTR1 levels were restored by infection with a lentivirus expressing wild-type CTR1 was reduced by a single maximum tolerated dose of DDP in vivo, whereas the CTR1(-/-) xenografts failed to respond at all. We conclude that CTR1 mediates the initial influx of DDP, CBDCA, and L-OHP and is a major determinant of responsiveness to DDP both in vitro and in vivo.

Carrier Recovery Enhancement for Maximum-Likelihood Doppler Shift Estimation in Mars Exploration Missions

One of the most crucial stages of the Mars exploration missions is the entry, descent, and landing (EDL) phase. During EDL, maintaining reliable communication from the spacecraft to Earth is extremely important for the success of future missions, especially in case of mission failure. EDL is characterized by very deep accelerations, caused by friction, parachute deployment and rocket firing among others. These dynamics cause a severe Doppler shift on the carrier communications link to Earth. Methods have been proposed to estimate the Doppler shift based on Maximum Likelihood. So far these methods have proved successful, but it is expected that the next Mars mission, known as the Mars Science Laboratory, will suffer from higher dynamics and lower SNR. Thus, improving the existing estimation methods becomes a necessity. We propose a Maximum Likelihood approach that takes into account the power in the data tones to enhance carrier recovery, and improve the estimation performance by up to 3 dB. Simulations are performed using real data obtained during the EDL stage of the Mars Exploration Rover B (MERB) mission.

Skip Entry Trajectory Planning and Guidance

A numerical predictor-corrector method for trajectory planning and closed-loop guidance of low-L/D vehicles during the skip entry phase of a lunar-return mission is presented. The strategy calls for controlling the trajectory by modulation of the magnitude of the vehicle's bank angle. The magnitude of the bank angle used in the skip phase is determined by satisfying the downrange requirement to the landing site. The problem is formulated as a nonlinear univariate root-finding problem. Full three-degree-of-freedom nonlinear trajectory dynamics are included to achieve high accuracy of the landing prediction. In addition, the proposed approach automatically yields a direct-entry trajectory when the downrange is such that a skip entry is no longer necessary. The same algorithm repeatedly applied onboard in every guidance cycle realizes closed-loop guidance in the skip entry phase. A number of issues are identified and addressed that are critical in closed-loop implementations. Extensive three-degree-of-freedom dispersion simulations are performed to evaluate the performance of the proposed approach, and the results demonstrate very reliable and robust performance of the algorithm in highly stressful dispersed conditions.

Enteroviruses receptors and cell entry

Human enteroviruses, which belong to the family of Picornaviridae, are common infectious viral agents transmitted by fecal-oral or airway routes. These positive RNA viruses possess a high genetic diversity and variability. They can evolve through genetic mutations or recombination mechanisms that are associated to the emergence of new potential epidemic serotypes. Human enteroviruses use different cellular receptors: receptors and co-receptors that are directly related to the tropism and the epidemiologic characteristics of some enterovirus serotypes. The receptors onto the cell-surface settle within a capsid depression, called canyon, initiating the process of viral uncoating. For some enteroviruses, a co-receptor molecule allows the crossing of cell topological barriers that is required to initiate the target cell infection. After the attachment phase, enteroviruses use the endocellar signaling pathways to support and optimize their entry into target-cells via endocytic pathways. The clathrin coated pits and the caveolae are both major ways of enterovirus entry in the cell even if "new" endocytic pathways regulated by enzymes of theADP ribosylation factors family and of the Rho family small GTPases have been recently described. The viral genetic diversity allows the human enteroviruses to simultaneously or alternatively use several distinct endocytic pathways in accordance to the infected cell lines, and allows a rapid and efficient adaptation to cellular microenvironments and to multiple immune selection pressures developed during the pathophysiological course of human infection. In conclusion, entry mechanisms used by human enteroviruses to infect target cells are various but they are closely dependent on the cellular functions that will be driven towards viral benefits. In the present time, the attachment and entry phases of the human enteroviruses into the target cell represent major viral events that may be targeted for the development of further new antiviral strategies.

Arrangement of L2 within the Papillomavirus Capsid

Papillomaviruses are a family of nonenveloped DNA tumor viruses. Some sexually transmitted human papillomavirus (HPV) types, including HPV type 16 (HPV16), cause cancer of the uterine cervix. Papillomaviruses encode two capsid proteins, L1 and L2. The major capsid protein, L1, can assemble spontaneously into a 72-pentamer icosahedral structure that closely resembles native virions. Although the minor capsid protein, L2, is not required for capsid formation, it is thought to participate in encapsidation of the viral genome and plays a number of essential roles in the viral infectious entry pathway. The abundance of L2 and its arrangement within the virion remain unclear. To address these questions, we developed methods for serial propagation of infectious HPV16 capsids (pseudoviruses) in cultured human cell lines. Biochemical analysis of capsid preparations produced using various methods showed that up to 72 molecules of L2 can be incorporated per capsid. Cryoelectron microscopy and image reconstruction analysis of purified capsids revealed an icosahedrally ordered L2-specific density beneath the axial lumen of each L1 capsomer. The relatively close proximity of these L2 density buttons to one another raised the possibility of homotypic L2 interactions within assembled virions. The concept that the N and C termini of neighboring L2 molecules can be closely apposed within the capsid was supported using bimolecular fluorescence complementation or "split GFP" technology. This structural information should facilitate investigation of L2 function during the assembly and entry phases of the papillomavirus life cycle.