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651.
M B Farber 《Journal of virology》1976,17(3):1027-1037
Bacteriophage phi X 174 gene D product, a protein required for single-stranded DNA synthesis by the phage, has been purified to near homogeneity. The protein is very abundant; approximately 10(5) monomers are present per infected cell when lysis is delayed. The protein has a monomer molecular weight of 15,200 and is normally a tetramer; however, it can form very large aggregates at high concentrations. Amino acid analysis shows an excess of arginine over lysine and a relatively high number of nonpolar residues. The protein carries a net negative charge at neutral pH. The first eight amino acids of the protein sequence have been determined; they are Ser-Gln-Val-Thr-Glu-Gln-Arg-Val. The carboxy-terminal residue is methionine. The protein has not yet been shown to bind directly to any single-stranded DNA; it does not adsorb to denatured calf thymus DNA-cellulose. 相似文献
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The suckling opossum exhibits an expiration-phased discharge in abdominal muscles during positive-pressure breathing (PPB); the response becomes apparent, however, only after the 3rd-5th wk of postnatal life. The purpose of this study was to determine whether the early lack of activation represented a deficiency of segmental outflow to abdominal muscles or whether comparable effects were observed in cranial outflows to muscles of the upper airways due to immaturity of afferent and/or supraspinal pathways. Anesthetized suckling opossums between 15 and 50 days of age were exposed to PPB; electromyogram (EMG) responses in diaphragm and abdominal muscles were measured, along with EMG of larynx dilator muscles and/or upper airway resistance. In animals older than approximately 30 days of age, the onset of PPB was associated with a prolonged expiration-phased EMG activation of larynx dilator muscles and/or decreased upper airway resistance, along with expiratory recruitment of the abdominal muscle EMG. These effects persisted as long as the load was maintained. Younger animals showed only those responses related to the upper airway; in fact, activation of upper airway muscles during PPB could be associated with suppression of the abdominal motor outflow. After unilateral vagotomy, abdominal and upper airway motor responses to PPB were reduced. The balance between PPB-induced excitatory and inhibitory or disfacilitory influences from the supraspinal level on abdominal motoneurons and/or spinal processing of information from higher centers may shift toward net excitation as the opossum matures. 相似文献
654.
Several fundamental questions remain enigmatic concerning human olfactory
sensitivity, including (i) whether detection threshold differences exist
between the two sides of the nose (and, if so, whether such differences are
influenced by handedness) and (ii) whether bilateral (i.e. binasal)
stimulation leads to lower thresholds than unilateral stimulation (and, if
so, whether the degree of facilitation is inversely related to general
olfactory ability). In this study, and well-validated single staircase
procedure was used to establish bilateral and unilateral detection
thresholds for the cranial nerve I stimulant phenyl ethyl alcohol in 130
right- and 33 left-handed subjects. No differences in sensitivity between
the left and right sides of the nose were observed in either group.
Bilateral thresholds were lower, on average, than unilateral thresholds
when the latter were categorized in terms of left and right nares. However,
the bilateral thresholds did not differ significantly from those of the
side of the nose with the lower threshold. Overall smell ability, as
measured by the University of Pennsylvania Smell Identification Test, did
not interact with any of the test measures. These data imply that (i) the
left and right sides of the nose do not systematically differ in detection
threshold sensitivity for either dextrals or sinistrals and (ii) if central
integration of left:right olfactory threshold sensitivity occurs, its
effects do not exceed the function of the better side of the nose.
相似文献
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658.
Clonal adaptation as an important phase of hepatocarcinogenesis. 总被引:2,自引:0,他引:2
E Farber 《Cancer biochemistry biophysics》1991,12(3):157-165
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