Area V4, a visuotopically organized area in prestriate cortex of the macaque, is the major source of visual input to the inferior temporal cortex, known to be crucial for object recognition. To examine the selectivity of cells in V4 for stimulus form, we quantitatively measured the responses of 322 cells to bars varying in length, width, orientation, and polarity of contrast, and sinusoidal gratings varying in spatial frequency, phase, orientation, and overall size. All of the cells recorded in V4 were located on the lower portion of the prelunate gyrus. Receptive fields were located almost exclusively within the representation of the central 5 degrees of the lower visual field, and receptive field size, in linear dimension, was 4-7 times greater than that in the corresponding representation of striate cortex (V1). Nearly all receptive fields consisted of overlapping dark and light zones, like "classic" complex fields in V1, but the relative strengths of the dark and light zones often differed. A few cells responded exclusively to light or dark stimuli. Many cells in V4 were selective for stimulus orientation, and a few were selective for direction of motion as well. Although the median orientation bandwidth of the orientation-selective cells (52 degrees) was wider than that reported for oriented cells in V1, approximately 8% of the oriented cells had bandwidths of less than 30 degrees, which is nearly as narrow as the most narrowly tuned cells in V1. The proportion of cells selective for direction of motion (13%) was not markedly different from that reported in V1. The large majority of V4 cells were tuned to the length and width of bars, and the "shape" of the optimal bar varied from cell to cell, as has been reported for cells in the dorsolateral visual area (DL) of the owl monkey, a possible homologue of V4 in the macaque. Preferred lengths and widths varied independently from approximately 0.05 to 6 degrees, with the smallest preferred bars about the size of the smallest receptive fields in V1 and the largest preferred bars larger than any fields in V1. The relationship between the size of the optimal bar and the size of the receptive field varied from cell to cell. Some cells, for example, responded best to bars much narrower or shorter than the field, whereas other cells responded best to bars that filled (but did not extend beyond) the excitatory field in the length, width, or both dimensions.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulated by pH, membrane-anchored proteins E and M play a series of roles during dengue virus maturation and membrane fusion. Our atomic model of the whole virion from cryo electron microscopy at 3.5Å resolution reveals that in the mature virus at neutral extracellular pH, the N-terminal 20-amino acid segment of M (involving three pH-sensing histidines) latches and thereby prevents spring-loaded E fusion protein from prematurely exposing its fusion peptide. This M latch was fastened at an earlier stage, during maturation at acid pH in the trans-Golgi network. At a later stage, to initiate infection in response to acid pH in the late endosome, M releases the latch and exposes the fusion peptide. Thus, M serves as a multistep chaperone of E to control the conformational changes accompanying maturation and infection. These pH-sensitive interactions could serve as targets for drug discovery.

Construction of a complex virus may involve a hierarchy of assembly elements. Here, we report the structure of the whole human adenovirus virion at 3.6Å resolution by cryo-electron microscopy, revealing in situ atomic models of three minor capsid proteins (IIIa, VIII and IX), extensions of the major (penton base and hexon) capsid proteins, and interactions within three protein-protein networks. One network is mediated by protein IIIa within Group-of-Six (GOS) tiles – a penton base and its five surrounding hexons – at vertices. Another is mediated by ropes (protein IX) that lash hexons together to form Group-of-Nine (GON) tiles and bind GONs to GONs. The third, mediated by IIIa and VIII, binds each GOS to five surrounding GONs. Optimization of adenovirus for cancer and gene therapy could target these networks.

We have incorporated into planar lipid bilayer membranes a voltage-dependent, anion-selective channel (VDAC) obtained from Paramecium aurelia. VDAC-containing membranes have the following properties: (1) The steady-state conductance of a many-channel membrane is maximal when the transmembrane potential is zero and decreases as a steep function of both positive and negative voltage. (2) The fraction of time that an individual channel stays open is strongly voltage dependent in a manner that parallels the voltage dependence of a many-channel membrane. (3) The conductance of the open channel is about 500 pmho in 0.1 to 1.0 M salt solutions and is ohmic. (4) The channel is about 7 times more permeable to Cl- than to K+ and is impermeable to Ca++. The procedure for obtaining VDAC; AND THE PROPERTIES OF THE CHANNEL ARE HIGHLY REPRODUCIBLE. VDAC activity was found, upon fractionation of the paramecium membranes, to come from the mitochondria. We note that the published data on mitochondrial Cl- permeability suggest that there may indeed be a voltage-dependent Cl- permeability in mitochondria. The method of incorporating VDAC into planar lipid bilayers may be generally useful for reconstituting biological transport systems in these membranes.

Vesicular stomatitis virus (VSV) is a bullet-shaped rhabdovirus and a model system of negative-strand RNA viruses. Based on direct visualization by cryo-electron microscopy, we show that each virion contains two nested, left-handed helices, an outer helix of matrix protein M and an inner helix of nucleoprotein N and RNA. M has a hub domain with four contact sites that link to neighboring M and N subunits, providing rigidity by clamping adjacent turns of the nucleocapsid. Side-by-side interactions between neighboring N subunits are critical for the nucleocapsid to form a bullet shape, and structure-based mutagenesis results support this description. Together, our data suggest a mechanism of VSV assembly in which the nucleocapsid spirals from the tip to become the helical trunk, both subsequently framed and rigidified by the M layer.

Spectral properties of 129 cells in the V4 area of 5 macaque monkeys were studied quantitatively with narrow-band and broad-band colored lights. The large majority of cells exhibited some degree of wavelength sensitivity within their receptive fields. The half-bandwidth of the primary peak in the spectral-response curve was less than 50 nm for 72% of the cells; the mean half-bandwidth of these cells, 27 nm, is similar to that found for color-opponent ganglion cells and cells in the parvocellular dorsal lateral geniculate nucleus (dLGN). Contrast-response functions indicated that the narrow spectral tuning of these cells derived from cone opponent interactions. From comparison of receptive-field sizes, we suggest that a typical V4 neuron sums inputs that ultimately derive from several thousand ganglion or parvocellular dLGN cells. In spite of their wavelength sensitivity, most V4 cells had properties that would not fit some simple criteria for classification as "color selective." First, few cells showed overt signs of color opponency, namely, on-inhibition or off-excitation to spectrally opponent wavelengths. Second, about 30% of the cells in V4 had spectral-response curves with 2 peaks. (The wavelength distribution of these second peaks was almost identical to that of primary peaks, and combinations of peak wavelengths were fairly random.) Third, most cells responded to white light; overall, the response to white light was about 60% of that to the best narrow-band or broad-band colored light. Similarly, most V4 cells gave at least a small response to all or nearly all of the different broad-band colored lights we presented. Therefore, a given V4 cell is very likely to respond to most of the colored or white surfaces in natural scenes. These combinations of response properties probably explain the widely divergent percentages of "color" cells reported in previous studies of V4. The most unusual spectral property we found in V4 was a large, spectrally sensitive surround outside the "classical receptive field" of most cells. Although stimulation of the surround by itself did not cause any response, surround stimulation could completely suppress the response to even the optimally colored stimulus in the receptive field. In general, the optimal wavelengths for receptive-field excitation and surround suppression were the same or nearly so. Thus, "color contrast" may be computed in V4. In some cases, contrasting wavelengths in the surround caused moderate enhancement of response to a receptive-field stimulus.(ABSTRACT TRUNCATED AT 400 WORDS)

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Visual acuity depends on the fine-grained neural image set by the foveal cone mosaic. To preserve this spatial detail, cones transmit through non-divergent pathways: cone-->midget bipolar cell-->midget ganglion cell. Adequate gain must be established along each pathway; crosstalk and sources of variation between pathways must be minimized. These requirements raise fundamental questions regarding the synaptic connections: (1) how many synapses from bipolar to ganglion cell transmit a cone signal and with what degree of crosstalk between adjacent pathways; (2) how accurately these connections are reproduced across the mosaic; and (3) whether the midget circuits for middle (M) and long (L) wavelength sensitive cones are the same. We report here that the midget ganglion cell collects without crosstalk either 28 +/- 4 or 47 +/- 3 midget bipolar synapses. Two cone types are defined by this difference; being about equal in number and distributing randomly in small clusters of like type, they are probably M and L.