姐妹染色单体互换在鹌鹑胚胎细胞染色体间及染色体上的分布

SCE在鹌鹑胚胎细胞间的分布为Poisson分布;在染色体间的分布是非随机的,与染色体的相对长度成正相关（P<0.05）,但也不完全按各染色体的相对长度分布。着丝粒区的SCE相对很高,按染色体的相对长度分布。胚胎的不同性别对每个细胞的SCE平均值无显著影响,但对性染色体Z上的SCE是否有影响还不能做出肯定的结论。     

The accessory middle cerebral artery--a variant of the recurrent artery of Heubner (A. centralis longa)?

Three accessory middle cerebral arteries are described in two out of 75 brains dissected under the operating microscope. Each artery originated from the anterior cerebral artery, lateral to its junction with the anterior communicating artery, followed the proximal segment (A1, pars precommunicalis) of the anterior cerebral artery, then the horizontal portion (M1, pars sphenoidalis) of the middle cerebral artery towards the lateral sulcus. Each supplied the lateral orbital gyrus, the gyrus longus of the insula, part of the putamen, the head of the caudate nucleus and the anterior limb of the internal capsule. The presence of the accessory middle cerebral artery is discussed with regard to the recurrent artery of Heubner (A. recurrens, A. centralis longa).     

NMR, CD and IR spectroscopies of a tridecanucleotide containing a no-base residue: coexistence of B and Z conformations.

The synthesis of the tridecadeoxynucleotide d(CGm5CGCGxACATGT), where x is the 1-cyano-2-deoxy-beta-D-erythropentofuranose, is described. The NMR, IR, CD studies at various salt concentrations and temperatures of this oligomer show that the B and Z conformations are simultaneously present in the same short DNA fragment. A single apurinic residue is sufficient for the coexistence of the B and Z helices on this oligomer.     

利用TMV—U1作为载体表达鼠肝炎病毒S糖蛋白片段

为了验证转基因烟草中表达的外壳蛋白（ＣＰ）能够重新包被侵入的烟草花叶病毒（ＴＭＶ）的假设,利用抗原表位标记的方法观察ＣＰ亚单位在病毒５′端的交换。通过ＰＣＲ 方法将来源于鼠肝炎病毒（ＭＨＶ） Ｓ蛋白的两个小肽段（１１ ａ．ａ．和１５ ａ．ａ．）的ＤＮＡ序列分别插入ＴＭＶ－Ｕ１ ＣＰ基因邻近３′端的两个位点,并构建了带有外源序列的ＴＭＶ 侵染克隆Ｖ９ （１１ ａ．ａ．）和Ｅ１５ （１５ ａ．ａ．）。通过体外转录反应,得到Ｖ９ ＲＮＡ 及Ｅ１５ ＲＮＡ。突变病毒ＲＮＡ 侵染烟草（Ｎｉｃｏｔｉａｎａ ｔａｂａｃｕｍ ）后表现不同特性。Ｖ９ 和Ｅ１５ 侵染ＸａｎｔｈｉＮＮ烟草后同野生型ＴＭＶ一样产生枯斑。但是,当它们侵染Ｘａｎｔｈｉｎｎ 烟草时,Ｖ９ 产生同侵染ＸａｎｔｈｉＮＮ 烟草相同的枯斑,而Ｅ１５的特性同ＴＭＶ－Ｕ１几乎完全相同,能对Ｘａｎｔｈｉｎｎ 烟草进行系统侵染并在叶片中聚集大量的带有外源片段的外壳蛋白,而且病毒的结构极其稳定。Ｖ９ 和Ｅ１５ 特性的差异可能是由于外源片段在外壳蛋白中存在位置的不同影响了外壳蛋白的结构所致     

DNA fragment conformations. A 1H-NMR conformational analysis of the d(G-G)-chelated platinum-oligonucleotide d(A-T-G-G)cisPt

The conformation of d(A-T-G-G) and d(A-T-G-G)cisPt has been investigated by 1H-NMR at 500 MHz and 90 MHz under various experimental conditions of temperature and concentration. Analysis of the coupling constants between the deoxyribose protons shows that all the sugar rings of d(A-T-G-G) adopt the S(C2'-endo) conformation most of the time. By contrast, in the platinated tetramer, d(A-T-G-G)cisPt, the N(C3'-endo) conformation is highly predominant for the internal dG residue while the S(C2'-endo) conformation is largely favoured for the other residues as in the case of the unplatinated compound. The relaxation time and nuclear Overhauser effect measurements indicate that the orientation of the two guanines of d(A-T-G-G)cisPt is anti in agreement with the previous results obtained for the dimers: r(G-G)cisPt, d(G-G)cisPt. On lowering the temperature from 80 degrees C to 20 degrees C, several proton resonances of d(A-T-G-G)cisPt exhibit large chemical shift and linewidth variations. The most spectacular temperature effect was observed for the internal dG(H1') and dT(H4') protons. All the delta = f(t) curves display a sigmoid form with the same mid-point temperature of 44 +/- 2 degrees C. This mid-point temperature together with the observed chemical shift and linewidth variations were found to be independent of the d(A-T-G-G)cisPt concentration. These results suggest that d(A-T-G-G)cisPt can adopt two different conformations depending on the temperature. The enthalpy for the transition between the high and low temperature conformations is about 84 kJ/mol.     

Proton NMR study of the B----Z transition of d(CGm5CG)2 and d(CGm5CGCG)2: theory and experiment.

The magnetic shielding produced by the double helix in a B-DNA and a Z-DNA conformation is calculated for each non exchangeable proton of the oligodeoxynucleotides d(CGm5CG)2 and d(CGm5CGCG)2. The differences between the values obtained for the two helical forms are in good agreement with the variations of chemical shift measured when the salt concentration of the solution is changed from 0.1 M to 2 or 4 M. The analysis of the theoretical chemical shift variations shows that the large upfield shift observed for some of the protons of the cytidine residues is due to the sum of the ring current and local magnetic anisotropy effects of the guanines of the two nearest neighbours residues.     

Genetic control of the primary humoral response to Glu56Lys35Phe9

The primary humoral responses of mice to the linear random terpolymerl-Glu⁵⁶-l-Lys³⁵-l-Phe⁹ (GLø) were studied, utilizing the Farr antigen-binding technique and a new hemagglutination assay. This new hemagglutinin assay was easier and more convenient than the conventional Farr method, and was more sensitive in detecting early IgM responses. Following primary immunization, the majority of antibodies produced by responder strains were 2-ME-sensitive. These 2-ME-sensitive antibodies chromatographed at the same relative position as IgM on a Sepharose 6B column. On the other hand, no antibodies of either the IgM or IgG class could be detected in nonresponder strains. These data are consistent with the hypothesis that two complementingIr genes are required for the primary IgM response to GLø, in contrast to findings previously reported for (T,G)-A — L, anotherH-2-linked, complementing,Ir gene system. The implications of these differences are discussed.     

C-nuclear magnetic resonance studies of 85% C-enriched amino acids and small peptides: pH effects on the chemical shifts, coupling constants, kinetics of cis-trans isomerisation and conformation aspects

The ¹³C chemical shifts of several 85% ¹³C-enriched amino acids and small peptides were studied as a function of pH. The results show that the chemical shifts of carbon atoms of ionizable groups vary significantly within the zone of their pK. Generally with the pH going from 7 to 1 all the δC are shifted more or less upfield with the exception of the carbonyl group of the second last residue which is shifted slightly downfield. This suggests the formation of an hydrogen bond at acid pH involving in a seven-membered ring the C=O in question and the COOH terminal.The percentage of cis and trans conformers of glycyl-l-proline and glycyl-l-prolylglycine were studied as a function of pH. The trans form is always preponderant whatever the pH. The accessibility of the carbonyl group to protonation of the proline residue strongly influences the cis-trans equilibrium. Thus, with the pH varying from 7 to 1, the trans isomer changes from 61 to 85% for glycyl-l-proline and only from 77 to 80% for glycyl-l-prolylglycine.The proton NMR studies underline the important differences existing between the two molecular forms of glycyl-l-proline. The cis conformation is characterized with regard to the trans form by the non-equivalence of the α-protons of the glycine residue, by a lower pK₁ and by a larger ΔδH_α of the proline residue as a function of pH. These results could suggest an end-to-end interaction in the cis form of the glycyl-l-proline molecule.The ¹³C-¹³C coupling constants were also studied as a function of pH. The results show that J_Co-Cα of a C-terminal residue, varying from 5 to 6 Hz and reflecting the pK of the carboxylate group, is a linear function of δ_Co and δ_Cα as in the case of the amino acids. The total variation of the electron density of those two carbons in an amino acid is approximately 40% weaker than in a C-terminal residue. The charge distribution along the C_α−C_o bond, however, is practically the same in both cases.Finally the ratios of the conversion rate constants of the two isomers cis-trans of glycyl-proline were calculated at different pH values; the relations between the isomer percentages and δ_Co, δ_Cα on the one hand and the J_Co-Cα on the other were established.     

Tillering and small grain 1 dominates the tryptophan aminotransferase family required for local auxin biosynthesis in rice

Auxin is a crucial phytohormone, controlling multiple aspects of plant growth and responses to the changing environment. However, the role of local auxin biosynthesis in specific developmental programs remains unknown in crops. This study characterized the rice tillering and small grain 1 (tsg1) mutant, which has more tillers but a smaller panicle and grain size resulting from a reduction in endogenous auxin. TSG1 encodes a tryptophan aminotransferase that is allelic to the FISH BONE (FIB) gene. The tsg1 mutant showed hypersensitivity to indole‐3‐acetic acid and the competitive inhibitor of aminotransferase, L‐kynurenine. TSG1 knockout resulted in an increased tiller number but reduction in grain number and size, and decrease in height. Meanwhile, deletion of the TSG1 homologs OsTAR1, OsTARL1, and OsTARL2 caused no obvious changes, although the phenotype of the TSG1/OsTAR1 double mutant was intensified and infertile, suggesting gene redundancy in the rice tryptophan aminotransferase family. Interestingly, TSG1 and OsTAR1, but not OsTARL1 and OsTARL2, displayed marked aminotransferase activity. Meanwhile, subcellular localization was identified as the endoplasmic reticulum, while phylogenetic analysis revealed functional divergence of TSG1 and OsTAR1 from OsTARL1 and OsTARL2. These findings suggest that TSG1 dominates the tryptophan aminotransferase family, playing a prominent role in local auxin biosynthesis in rice.