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21.
Unlikelihood that minimal phylogenies for a realistic biological study can be constructed in reasonable computational time 总被引:1,自引:0,他引:1
R. L. Graham 《Mathematical biosciences》1982,60(2):133-142
The problem of determining a phylogeny of maximum parsimony from a given set of protein sequences is defined. It is shown that this problem is what is called, in computer science, NP-complete. The implication of this result is that it is equivalent in difficulty to a host of other problems in combinatorial optimization which are notorious for their intractability. This implies that it is more fruitful to attempt to develop heuristic techniques (which do not guarantee maximum parsimony but which do run in reasonable computer time) than to try to develop exact algorithms for phylogeny construction 相似文献
22.
A numerical taxonomic study of strains of Actinobacillus, Pasteurella and Yersinia, with some allied bacteria, showed 23 reasonably distinct groups. These fell into three major areas. Area A contained species of Actinobacillus and Pasteurella: A. suis, A. equuli, A. lignieresii, P. haemolytica biovar A, P. haemolytica biovar T, P. multocida, A. actinomycetemcomitans, 'P. bettii', 'A. seminis', P. ureae and P. aerogenes. Also included in A was a composite group of Pasteurella pneumotropica and P. gallinarum, together with unnamed groups referred to as 'BLG', 'Mair', 'Ross' and 'aer-2'. Area B contained species of Yersinia: Y. enterocolitica, Y. pseudotuberculosis, Y. pestis and a group 'ent-b' similar to Y. enterocolitica. Area C contained non-fermenting strains: Y. philomiragia, Moraxella anatipestifer and a miscellaneous group 'past-b'. There were also a small number of unnamed single strains. 相似文献
23.
The oxidants of the SH groups (o-iodozobenzoate, oxidized glutathione, etc.) and the divalent cations of some metals (Zn2+ and Cd2+) significantly slow down the rate of inactivation by the protein inhibitor of the isolated F1-ATPase and ATPase in submitochondrial particles. Modification of SH groups in the ATPase does not change the rate of inactivation but completely prevents the effect of oxidants. 相似文献
24.
H. G. Kilian M. Kazda F. Király D. Kaufmann R. Kemkemer D. Bartkowiak 《Cell biochemistry and biophysics》2010,57(2-3):87-100
If growing cells in plants are considered to be composed of increments (ICs) an extended version of the law of mass action can be formulated. It evidences that growth of plants runs optimal if the reaction–entropy term (entropy times the absolute temperature) matches the contact energy of ICs. Since these energies are small, thermal molecular movements facilitate via relaxation the removal of structure disturbances. Stem diameter distributions exhibit extra fluctuations likely to be caused by permanent constraints. Since the signal–response system enables in principle perfect optimization only within finite-sized cell ensembles, plants comprising relatively large cell numbers form a network of size-limited subsystems. The maximal number of these constituents depends both on genetic and environmental factors. Accounting for logistical structure–dynamics interrelations, equations can be formulated to describe the bimodal growth curves of very different plants. The reproduction of the S-bended growth curves verifies that the relaxation modes with a broad structure-controlled distribution freeze successively until finally growth is fully blocked thus bringing about “continuous solidification”. 相似文献
25.
S V Prozorovski? L P Tsarevski? G A Levina A L Gorelov 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1985,(8):10-14
To simulate the infectious process and to study the persistence of L-forms, rabbits and guinea pigs were infected with S. typhi stable L-forms. The materials presented in this work indicate that both subconjunctival and intraperitoneal infection led to the development of the clinically indistinct, but morphologically pronounced pathological process with characteristic localization and typical changes in the gastrointestinal tract. The typical features of the process were the generalized immunomorphological reaction of the lymphoid apparatus with the appearance of light-colored reticulomacrophagal elements, the signs of the activation of humoral and cell-mediated immunity and the formation of small epitheloidocellular granulomas. The results of the investigation indicate that the stable cultures of S. typhi L-forms are highly pathogenic and capable of inducing the infectious process in experimental animals. 相似文献
26.
L. N. GILLMAN D. J. KEELING R. C. GARDNER S. D. WRIGHT 《Journal of evolutionary biology》2010,23(6):1327-1330
A faster rate of nuclear DNA evolution has recently been found for plants occupying warmer low latitudes relative to those in cooler high latitudes. That earlier study by our research group compared substitution rates within the variable internal transcribed spacer (ITS) region of the ribosomal gene complex amongst 45 congeneric species pairs, each member of which differed in their latitudinal distributions. To determine whether this rate differential might also occur within highly conserved DNA, we sequenced the 18S ribosomal gene in the same 45 pairs of plants. We found that the rate of evolution in 18S was 51% faster in the tropical plant species relative to their temperate sisters and that the substitution rate in 18S correlated positively with that in the more variable ITS. This result, with a gene coding for ribosomal structure, suggests that climatic influences on evolution extend to functionally important regions of the genome. 相似文献
27.
B B Fuks N F Avrova L V Van'ko N A Starosvetskaia M N Boltovskaia 《Biulleten' eksperimental'no? biologii i meditsiny》1986,101(1):66-68
Female BALB/c mice were immunized with human melanoma (Mewo) cells containing ganglioside GD3 as a surface antigen. Immune splenocytes were fused with syngeneic P3-X63.Ag 8 myeloma cells. Antibodies produced by hybrid clones were analyzed by solid phase immunoassay. B, C, D and Q clones producing antibodies against Raja clavata brain gangliosides were obtained. Monoclonal B and C antibodies bound monosialogangliosides. Monoclonal D antibody bound a number of gangliosides but reacted predominantly with GD1a. Monoclonal Q antibody reacted selectively with GQ1c. It is assumed that ganglioside GQ1c is expressed on the melanoma cell surface and may be found only in the early stage of ontogenesis of high vertebrates. 相似文献
28.
L J Petterborg M K Vaughan L Y Johnson T H Champney R J Reiter 《Comparative biochemistry and physiology. A, Comparative physiology》1984,78(1):31-34
Exposure of male Syrian hamsters (Mesocricetus auratus) for 10 weeks to short photoperiod (SP) providing 10 hr light: 14 hr darkness (10:14 LD) produced a significant reduction in the weights of the reproductive organs, plasma thyroxine (T4) levels and free T4 index (FT4I) compared to the values of animals exposed to long photoperiod (LP, 14:10 LD). C57bl male house mice (Mus musculus) kept in SP (10:14 LD) had reproductive organ weights equivalent to those of mice kept in long days (14:10 LD) and lower T3 uptake (T3U) values. Male gerbils (Meriones unguiculatus) exposed to 13 weeks of SP (10:14 LD) had lower body weights, testes and seminal vesicle weights and higher T3U values compared to LP (14:10 LD) controls. However, no effect was seen on plasma T4 and triiodothyronine (T3) values nor the FT4I and free T3 index (FT3I). White-footed male mice (Peromyscus leucopus) exposed to SP (8:16 LD) had significantly lower testes and seminal vesicle weights while plasma T4 and T3 levels were unaffected. Snell strain house mice (Mus musculus) exposed to SP (8:16 LD) had normal reproductive organ weights compared to the values of LP-exposed (16:8 LD) control animals. However, there was a significant depression in T3 and in the FT3I in the SP animals. 相似文献
29.
Airway area by acoustic reflections measured at the mouth 总被引:5,自引:0,他引:5
Fredberg J. J.; Wohl M. E.; Glass G. M.; Dorkin H. L. 《Journal of applied physiology》1980,48(5):749-758
30.
Cultured Friend murine erythroleukemia cells (Friend cells) are induced to undergo erythroid differentiation when grown in the presence of dimethylsulfoxide (DMSO) and other compounds. The effects of unifilar substitution of bromouracil (BU) for thymidine in the DNA (BU-DNA) of Friend cells were examined. Cells were grown in the presence of 5-bromodeoxy-uridine (BrdU) for one generation, then centrifuged and resuspended in medium containing DMSO without BrdU. These cells exhibited a delay in the appearance of heme-producing, benzidine-reative (B+) cells and a decreased rate of cell proliferation in comparison to the control not containing BU-DNA. A transient inhibition of entry into S phase was observed when control cells or cells containing BU-DNA were grown in the presence of DMSO) for 10 to 20 hours. This transient inhibition was increased in the BrdU culture. Thus BU-substitution in Friend cells alters other cellular functions in addition to erythroid differentiation. The rate of increase in the percent of cells committed to differentiate (those forming B+ colonies in plasma clots) was similar in the BrdU and control cultures until 40 to 50 hours. After this time, a delay in the appearance of committed cells was observed in the BrdU culture. The effect of BrdU on the appearance of B+ cells was more pronounced and occurred earlier than its effect on the rate of commitment. Therefore, the delay in the appearance of B+ cells in the BrdU culture was due primarily to perturbation of post-commitment events such as the accumulation of hemoglobin. We also examined the effect on growth and differentiation after BrdU was incorporated during different intervals of S phase in cells synchronized by centrifugal elutriation or by double thymidine block and hydroxyurea treatment. The delay in the appearance of B+ cells and inhibition of cell proliferation were only observed when BrdU was incorporated in the first half of S phase. BrdU (10 muM) had no effect on growth or differentiation when present during late S or G1 and G2. These results, using two very different methods to achieve cell synchrony, indicate that the effects of BrdU on growth and differentiation described above are due to its incorporation into DNA sequences replicating during early S. 相似文献