Computer search of calcium binding sites in a gene data bank: use of learning techniques to build an expert system

Using a learning set of 28 sequences able to bind calcium (each sequence is 12 residues long), we have built two filters by learning on this set. The first filter uses a pattern-matching technique and the second one takes into account the environment of amino-acids. These two filters have been used to find new calcium-binding proteins in a data bank. The results are discussed.     

Utilisation de lois de la mécanique pour l'Estimationde la vitesse de locomotion des Vertébrés tétrapodes du passé

Two computation methods are explained; theirobject is the estimation of the velocity of animals which are known by their footprints, and in the case of the first method, by their skeletons as well.The first method is based on the compound pendulum theory, because during the slow walking gait, the motion of the leg is similar to the oscillation of a pendulum, for the computation of the velocity (v), are considered: moment of inertia (I), radius of gyration (P) and period (T), time in seconds to cover one stride (E) in the case the maximum angle of divarication (δ) of the leg with the vertical is ≤20°. A comparison with the formula of Alexander (1976) is discussed.The second method concerns saltator animals. It is based on the fondamental laws of dynamics. With the length of the jump (E) it is possible to estimate the velocity of the trackmaker (v) and the height of the jump (K). For the vertebrates the angle of the trajectory with the horizontal plan (α) is between 20 and 45°. Thus, the result of this method is an interval of estimation in which the velocity is included.These methods do not give precise results. But these approximations supply valid informations on the velocity of extinct or living animals and can lead to the estimation of their maximum speed if the parameters E, T, vary. The problem of the errors is also discussed. It is shown that the errors in estimating the parameters have a no significant influence on the results.     

Unsuccessful induction of low-zone tolerance to bovine serum albumin injected into the subarachnoid space

Introduction of T-dependent antigens into the subarachnoid space (isas) resulted in higher systemic antibody responses in mice than injections into the peritoneal cavity (ip) or other sites commonly used for immunization. Antibody production in isas immunized mice was not increased by treatment with cyclophosphamide (Cy) at doses known to abolish T-suppressor-cell activity, but such treatment increased antibody production in ip immunized mice toward the higher level which was observed in the isas immunized animals. Suppressor cell-dependent low zone tolerance (LZT) to TNP-BSA could not be induced by isas injections of deaggregated BSA (d-BSA). Conversely, mice which were unresponsive to ip injected d-BSA showed consistent systemic antibody responses when the antigen was injected isas. These observations indicate that immune responses initiated within the CNS are associated with relatively ineffective induction of systemic suppressor cell activity.     

Nonrandomness of point mutation as reflected in nucleotide substitutions in pseudogenes and its evolutionary implications

Summary We have obtained a revised estimate of the pattern of point mutation by considering more pseudogene sequences. Compared with our previous estimate, it agrees better with expectations based on the double-strand structure of DNA. The revised pattern, like the previous one, indicates that mutation occurs nonrandomly among the four nucleotides. In particular, the proportion of transitional mutations (59%) is almost twice as high as the value (33%) expected under random mutation. The same high proportion of transitions is observed in synonymous substitutions in genes. The proportion of transitional changes observed among electrophoretic variants of human hemoglobin is about the same as that predicted by the revised pattern of mutation. We also show that nonrandom mutation increases, by about 15%, the proportion of synonymous mutations due to single-nucleotide changes in the codon table, and increases, from 10% to 50%, the rate of synonymous mutation in the seven genes studied. However, nonrandom mutation reduces (by about 10%) the proportion of polar changes among nonsynonymous mutations in a gene. As far as single-nucleotide changes (in the codon table) are concerned, nonrandom mutation only slightly favors relatively conservative amino acid interchanges, and has virtually no effect on the proportions of radical changes and nonsense mutations.     

^60Co—γ射线诱导的小麦T型雄性不育系育性恢复突变

用~(60)Co-γ射线诱导小麦T型雄性不育系T小偃4号A、T郑引1号A均获得了农艺性状优良、恢复力强的恢复系。育性恢复突变是涉及一个或少数几个位点核基因的显性突变。利用性状优良的T型不育系诱导育性恢复突变是选育恢复系和发掘恢复源的有效途径。     

Induction of ?2 frameshift mutations within alternating GC sequences by carcinogens that bind to the C8 position of guanine residues Development of a specific mutation assay

Summary Using a forward mutation assay we have previously found that N-2-acetylaminofluorene (AAF), a strong chemical carcinogen, induces a majority of frameshift mutations located at specific sequences called mutation hot spots. Among these hot spot sequences, the NarI sequence (GGCGCC), is specific for –2 frameshifts (GGCGCC) GGCC). Interestingly, these frameshift mutations occur independently of a functional umuDC locus. Being interested in elucidating this mutation pathway we have developed a reversion assay that is specific for this class of mutations. The assay is based on the reversion of a +2 frameshift mutant of plasmid pBR322 from tetracycline sensitivity to tetracycline resistance. It is shown that only true reversion events lead to tetracycline resistance. The carcinogen AAF induces this reversion event at a frequency that is increased four- to fivefold over the background frequency. A series of chemical carcinogens which, like AAF, bind covalently to the C8 position of guanine, are compared for their efficiency to induce this specific mutation event. Large variations in the mutagenic efficiency of these chemicals are observed and discussed in terms of the anti/syn conformation of the carcinogen-modified guanine residue. Based on this test, we describe a convenient spot assay that this presently used in our laboratory to isolate Escherichia coli mutants affected in this mutation pathway.     

Relationship of vector insert size to homologous integration during transformation of Neurospora crassa with the cloned am (GDH) gene

Summary We used lambda and plasmid vectors containing the am ⁺ gene in an insert of from 2.7 to 9.1 kb, to transform am point mutant and deletion strains. A total of 199 transformants were examined with the potential to yield am ^– transformants by homologous recombination. When we used vectors that had 9.1 kb of homology with the chromosomal DNA, 30% of the transformants obtained were the result of homologous recombination regardless of whether the vector was a lambda molecule, a circular plasmid, or a plasmid that had been linearized prior to transformation. When vectors with up to 5.1 kb of homology were used, very few transformants (1 of 89 tested) resulted from homologous recombination. Of a sample of 29 ectopic integration events obtained by transformation with the 9.1 kb fragment cloned in a vector, 18 included a major part (usually almost all) of both arms of lambda with the entire Neurospora 9.1 kb insert between them. Four included only long arm sequence together with an adjacent segment of the insert containing the am gene. The remaining seven were the result of multiple integrations. There was no evidence of circularization of the vector prior to integration. All transformants that had multiple copies of the am gene appeared to be subject to the RIP process, which causes multiple mutations in duplicated sequences during the sexual cycle.     

Chloroplast DNA diversity in wild and cultivated species of rice (Genus Oryza,section Oryza). Cladistic-mutation and genetic-distance analysis

Summary Using a novel nonaqueous procedure, chloroplast DNA was isolated from 318 individual adult rice plants, representing 247 accessions and the breadth of the diversity in section Oryza of genus Oryza. Among them, 32 different cpDNA restriction patterns were distinguished using the restriction endonucleases EcoRI and AvaI, and they were further characterized by restriction with BamHI, HindIII, SmaI, PstI, and BstEII enzymes. The differences in the electrophoretic band patterns were parsimoniously interpreted as being the result of 110 mutations, including 47 restriction site mutations. The relationships between band patterns were studied by a cladistic analysis based on shared mutations and by the computation of genetic distances based on shared bands. The deduced relationships were compared with earlier taxonomical studies. The maternal parents for BC genome allotetraploids were deduced. Within species, cpDNA diversity was found larger in those species with an evolutionary history of recent introgression and/or allotetraploidization. Occasional paternal inheritance and recombination of cpDNA in rice was suggested.     

突变体——侏儒小鼠(dw~t)与津白3(TA3)不同日龄骨骼、体重及体长的比较

侏儒小鼠与津白3体重的比值为1:2.5。它们的骨骼、休重、休长及尾长的测量均具非常显著或显著意义。经均衡性检验,不同日龄、不同性别间TA3/dw~t小鼠的不同骨骼、体重、体长及尾长的比值变化是均匀一致的。证明侏儒小鼠骨骼、体重、体长及尾长均系均匀缩小,是身体各部分匀称的侏儒小鼠。