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31.
In mammalian cells, base pairing between the U2 and U6 small nuclear RNAs is required during pre-RNA splicing. We show by psoralen crosslinking of HeLa nuclear extract that U2.U6 base pairing occurs within abundant ribonucleoprotein complexes that sediment at > 150 S in glycerol gradients. All of the spliceosomal RNAs (U1, U2, U4, U5, and U6) cosediment with these large complexes, suggesting that they may be related to small nuclear RNA-containing structures called speckles/coiled bodies or snurposomes, which have been visualized in mammalian or amphibian nuclei, respectively. In contrast to nuclear extract, S100 extract, which is splicing-defective and lacks the > 150S complexes, does not contain base-paired U2.U6. However, U2.U6 base pairs form in S100 extract that has been made splicing-competent by supplementation with Ser/Arg-rich (SR) proteins, ATP, and an adenovirus splicing substrate. During splicing in supplemented S100 extract, U2.U6 base pairing precedes the appearance of splicing intermediates and occurs initially in an approximately 60S spliceosome complex but also in progressively larger (100-300 S) complexes. Possible functional relationships between the 60S spliceosome and the > 150S complexes are discussed. 相似文献
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DA Gray 《Canadian Metallurgical Quarterly》1997,54(6):1553-1562
This study demonstrates that invertebrate acoustic signals can provide information about male phenotypic attributes, and that females can use this acoustic information in mate choice to select a phenotypically superior mate. I investigated the relationships between a male acoustic sexual signal, the phenotype of the signaller, and the female response to signal variation. I recorded and analysed the calling songs of male house crickets, Acheta domesticus. The analyses showed that chirps convey information about male size. With the exception of amplitude, the mean number of pulses per chirp was the best predictor of male size. I performed a laboratory tape-playback experiment to determine female preference during phonotaxis. Females preferred tapes playing the chirps of large males, specifically chirps with a greater number of pulses per chirp. Selection on the female preference is discussed.Copyright 1997 The Association for the Study of Animal Behaviour 相似文献
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DA Bloch 《Canadian Metallurgical Quarterly》1997,53(1):73-85
Methods are proposed for comparing two diagnostic tests for the same data where a threshold for positive for each test is specified. One method contrasts the diagnostic tests' estimated risks. A second method compares the two tests' kappa coefficients. When thresholds for positive test results are specified a priori, maximum likelihood estimators and their asymptotic variances are derived and test statistics are presented for both case-control and naturalistic methods of sampling. The bootstrap is proposed as a method to assess differences in risk estimators when thresholds for positive test results are chosen by scanning the data. Examples are given to illustrate the methods. 相似文献
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The survival rate of patients admitted to the Royal Prince Alfred Hospital (RPAH) from the central Sydney area with a major injury has improved since regionalization of trauma services in early 1992. This improvement has been attributed to education, better hospital care and changing trauma epidemiology. This study was conducted to assess whether the outcome of patients admitted with haemorrhagic shock had improved. This is proposed as a more subtle indicator of hospital performance than overall survival rates. A prospective before and after study was carried out comparing outcome in the 18 months preceding 1 January 1992 with that in the subsequent 18 months. Entry criteria to the study included all primary retrievals from the central Sydney area to RPAH with injury severity scores (ISS) > 15. Outcomes were compared generally and in those who were in a state of haemorrhagic shock (systolic blood pressure < or = 90 mmHg) on arrival at the emergency department. Three hundred and eight patients were entered into the study. Stratification showed similar numbers, demographic features and mechanisms of injury in the two groups. Forty patients were in a state of haemorrhagic shock on admission. The overall mortality was reduced from 31% to 11% (P < 0.001) over the two phases of the study. The mortality from blood loss in the 40 shocked patients fell from 10/25 in the first period to 2/15 (P = 0.07) in the latter. These improved survival rates were felt to reflect the value of the educational and organizational initiatives introduced following designation of the hospital as a trauma centre. 相似文献
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The association of antiphospholipid antibodies with unexplained thrombo-occlusive vascular disease is well known but often remains unrecognized. The most well-studied clinical manifestation is venous thrombosis, but arterial occlusive disease involving multiple sites is also well documented. Twenty-six cases of thrombo-occlusive disease were observed in 22 patients over a 3-year period. Magnetic resonance imaging and angiography were used to make the diagnoses. None of the patients who underwent angiography or venography developed thrombolytic disease related to the puncture site. This group of patients with antiphospholipid antibody syndrome had a wide distribution of arterial and venous thrombotic disease. Radiologists should consider antiphospholipid antibody syndrome in the differential diagnosis when evaluating thrombo-occlusive vascular disease that is unexpected or occurs without risk factors. Knowledge of antiphospholipid antibody status has important implications for prognosis and therapy. 相似文献
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We have previously observed that bovine papillomavirus type 1 (BPV-1) induces the appearance of five cellular proteins in C127 mouse fibroblasts, four of which appear to arise by altered processing of resident endoplasmic reticulum proteins. Studies of various cell lines revealed that expression of the 3' end of the BPV early region was sufficient for induction of these changes. To identify the BPV gene responsible, we have utilized the simian virus 40 (SV40)/BPV-1 recombinant virus Pava-1, which expresses the 3' end of the BPV early region behind an SV40 early promoter. C127 cells infected with Pava-1 for 48 h show the expected BPV-associated alterations, as do cells infected with Pava constructs mutated in the E5 or E2 genes. However, a mutation in the start codon of a previously ignored open reading frame extending from nucleotides 4013 to 4170 (E5B) eliminated the BPV-associated changes. Similar results were obtained with COS cells infected with the Pava mutants and C127 cells transformed by full-length mutated BPV. Despite its influence on the processing of cellular endoplasmic reticulum proteins, this mutation in E5B did not alter BPV-transforming efficiency or the ability of transformants to form colonies in soft agar. The E5B open reading frame encodes a hydrophobic 52-amino-acid polypeptide that shares structural similarities with HPV6 E5A and HPV16 E5. Speculations on a role for E5B in the viral life cycle are discussed. 相似文献