A fast dynamic mode of the EF‐G‐bound ribosome

A key intermediate in translocation is an ‘unlocked state’ of the pre‐translocation ribosome in which the P‐site tRNA adopts the P/E hybrid state, the L1 stalk domain closes and ribosomal subunits adopt a ratcheted configuration. Here, through two‐ and three‐colour smFRET imaging from multiple structural perspectives, EF‐G is shown to accelerate structural and kinetic pathways in the ribosome, leading to this transition. The EF‐G‐bound ribosome remains highly dynamic in nature, wherein, the unlocked state is transiently and reversibly formed. The P/E hybrid state is energetically favoured, but exchange with the classical P/P configuration persists; the L1 stalk adopts a fast dynamic mode characterized by rapid cycles of closure and opening. These data support a model in which P/E hybrid state formation, L1 stalk closure and subunit ratcheting are loosely coupled, independent processes that must converge to achieve the unlocked state. The highly dynamic nature of these motions, and their sensitivity to conformational and compositional changes in the ribosome, suggests that regulating the formation of this intermediate may present an effective avenue for translational control.     

Pigments and ultrastructures of pigment cells in xanthic sailfin mollies (Poecilia latipinna).

Electron micrographs of skin from xanthic (gold) sailfin mollies revealed numerous xanthophores, as well as scattered melanophores. The melanophores were seen to contain premelanosomes in various stages of development. This is consistent with the fact that xanthic mollies have been shown to be tyrosinase positive. Melanosomes in xanthic mollies appear to develop by one of two pathways: 1) from an endoplasmic reticulum-derived vesicle which develops an internal lamellar framework, and 2) by fusion of multiple Golgi-derived vesicles which lack an internal lamellar framework. Analysis of the pigments in the skin of the xanthic mollies identified four colorless pteridine pigments (xanthopterin, isoxanthopterin, neopterin, and pterin) and a carotenoid with an absorbance spectrum similar to beta-carotene. It appears that, unlike some other poeciliid fishes, sailfin mollies do not use pteridine pigments for orange coloration. Rather, they appear to rely primarily on carotenoids.     

A preliminary investigation of prediction of mean arterial pressure after self-regulatory treatments.

This study investigated the ability of pretreatment variables from three different domains (social-demographic, psychological, and psychophysiological) to predict posttreatment mean arterial pressure (MAP) for 59 unmedicated males with mild hypertension who were participating in a cross-cultural (USA-USSR) comparison of autogenic training and thermal biofeedback to a self-relaxation control. The overall multiple regression equation consisted of two variables and indicated that higher diastolic blood pressures during a cold pressor task were predictive of greater MAP reductions while higher scores on the Irritability subscale of the Buss-Durkee Hostility Scale were predictive of less MAP reductions. Suggestions for future research in this area are provided.     

Crystallization and preliminary x-ray diffraction study of the flavoprotein NADH peroxidase from Streptococcus faecalis 10C1

NADH peroxidase from Streptococcus faecalis 10C1 has been crystallized from ammonium sulfate solutions using the hanging drop vapor diffusion method. Depending on pH, the crystals grew in the orthorhombic space group I222 or one of its subgroups P222 or P2(1)2(1)2 (or one of its two permutations). In both cases the unit cell axes are a = 76.6 A, b = 132.9 A, and c = 145.7 A. There are two monomers/asymmetric unit in the body-centered crystal form and four in the primitive one. The enzyme is catalytically active in the crystalline state. The crystals diffract to at least 2.5 A resolution; they are stable in the x-ray beam and hence suitable for detailed three-dimensional structure determination.     

Effects of semen fractionation and dilution ratio on equine spermatozoal motility parameters

Two experiments were conducted to examine the effects of semen fractionation and dilution ratio on motility parameters of stallion spermatozoa. In Experiment 1, three ejaculates from each of three stallions were divided into sperm-rich (SR) and sperm-poor (SP) fractions to determine the difference in sperm concentration. Mean sperm concentration in SR fractions (349.5 x 10(6)/ml) was greater (P < 0.001) than that of SP fractions (96.9 x 10(6)/ml). In Experiment 2, three ejaculates from each of two stallions were divided into SR and SP fractions. Fifty percent of the original volume of SR fractions was combined with 50% of the original volume of SP fractions for each ejaculate to represent total ejaculates. SR and total ejaculates were diluted with skim milk-glucose semen extender as follows: 1) no dilution, or dilution to 2) 100 x 10(6)sperm/ml, 3) 50 x 10(6)sperm/ml, or 4) 25 x 10(6)sperm/ml. Semen samples were evaluated at 0.5, 3, 6, 12, and 24 h postejaculation (25 degrees C storage temperature) for percentages of total spermatozoal motility (TSM) and progressive spermatozoal motility (PSM). Mean TSM was greater (P < 0.05) in SR ejaculates than total ejaculates at 12 and 24 h postejaculation. Mean TSM of undiluted semen was lower (P < 0.05) than other dilution ratios over all periods. Mean TSM was greater (P < 0.05) at a 25 x 10(6)sperm/ml dilution ratio than a 50 x 10(6)sperm/ml dilution ratio at 12 and 24 h postejaculation, and greater (P < 0.05) than a 100 x 10(6)sperm/ml dilution ratio from 3 to 24 h postejaculation. Similar patterns were found for PSM. Collection of SR ejaculates and dilution to 25 x 10(6)sperm/ml improved longevity of spermatozoal motility.     

Infectivity inhibition of HIV prototype strains by antibodies directed against a peptide sequence of mycoplasma

Antibodies prepared against a peptide corresponding to the site of cyto-adherence of Mycoplasma genitalium adhesine inhibit or reduce the infectivity of the HIV-1BRU and HIV-2ROD strains of Human Immunodeficiency Virus in lymphoid cells. These results strengthen the hypothesis that some mycoplasmas may play an important part in HIV replication and pathogenicity.     

Ureaplasma urealyticum urease genes; use of a UGA tryptophan codon

Nucleotide sequence analysis of a Ureaplasma urealyticum DNA fragment, homologous to cloned urease genes of other prokaryotes, revealed three consecutive open reading frames. The molecular weights of the three deduced polypeptides are 11.2 kD, 13.6 kD and 66.6 kD. These values are consistent with the size of the three subunits previously reported for purified native urease. A significant sequence homology was found between the three polypeptides of the ureaplasmal urease and the single polypeptide of jack bean (Canavalia ensiformis) urease. Codon usage indicates that UGA is a tryptophan codon in this mollicute. Use of polymerase chain reactions has disclosed the existence of genetic polymorphism among the urease genes of different serotypes of U. urealyticum.     

Dynamics of breathing in the hypoxic awake lamb

Newborn mammals respond to hypoxia with an immediate hyperventilation that is rapidly dampened. Changes in mechanical properties of the respiratory system during hypoxia have been considered an important reason for this fall in minute ventilation (VE). We have studied the dynamic mechanical behavior of the respiratory system in eight unanesthetized intact newborn lambs (mean age 2 days) during normoxia and hypoxia (FIO2 = 0.08). Mouth pressure (P), airflow (V), and volume (V) were recorded while lambs were breathing through a leak-proof face mask and a pneumotachograph. Active compliance (C') and resistance (R') of the respiratory system were computed from P developed during an inspiratory effort against airway closure at end expiration and V and V of the preceding breaths. Tidal expiratory V-V curves were analyzed to estimate the elevation in functional residual capacity (FRC) over resting volume (Vr). After hypoxia, there was an immediate increase in VE in the first 2 min, from 0.49 to 1.13 l.kg-1.min-1, followed by a rapid decrease to 0.80. After 8 min of hypoxia, C' was unchanged. The inspiratory R' decreased during hypoxia, probably reflecting a drop in inspiratory laryngeal resistance. The expiratory V-V curves during hypoxia showed considerable braking, often with a double peak in expiratory V. This pattern was only occasionally seen during normoxia. In animals with a linear segment of the expiratory V-V curves the FRC-Vr difference could be calculated and averaged 1.93 ml/kg during normoxia and 3.47 during hypoxia. The recoil P of the respiratory system at end expiration was 0.75 cmH2O during normoxia vs. 1.63 cmH2O during hypoxia (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)