共生菌Hebeloma sp.的线形质粒DNA的分子克隆及测序的研究

共生担子菌滑菇 H ebeloma circinas携带两个线形的染色体外 DNA分子 .全部的菌丝 DNA经蛋白酶 K处理后 ,通过琼脂凝胶电泳观察到 :在染色体 DNA旁有两个大小不等的 DNA带 ,命名为 p HCl和 p HC2 ,其分子量分别为 1 0 .3kb和 9.1 kb.用核酸外切酶处理 p HC DNA,确认其 5′端被保护 .对 p HC2用不同的内切酶处理并确定其内切酶图谱 ,对其 3.2 kb H ind 片段进行克隆 ,亚克隆和测序 .结果表明 :其片段有两个开读框 ( open reading frames) ,携带类似于病毒 B型的DNA和 RNA多聚酶基因编码 .p HC2为该菌携带的一个典型的线形质粒 ,这也是首次在共生担子菌中发现的线形质粒 .     

The Role of Compartmentalization in the Activation of Particular Control Genes and in the Generation of Proximo-Distal Positional Information in Appendages

SYNOPSIS. A mechanism is proposed for the activation of particulargenes during interpretation of positional information and duringsequential addition of new structures during outgrowth. Theprimary event is assumed to be an alternation between two states.The alternation of anterior-posterior-anterior compartmentsin insects or bone-joint-bone in the chicken wing is assumedto be a trace of this primary subdivision into two alternativestates. Each (or each second) transition from one state to theother causes a switch from one structure-controlling gene tothe next. This enables a counting of alternations on the DNA-leveland a high resolution in the corresponding activation of controlgenes. The model explains the formation of compartments andsegmental specification in perfect register. The elements ofthe bithorax gene complex become understandable assuming thismechanism. It is shown further that such a "compartmentalization" can beused for the reproducible generation of subpatterns for thefiner subdivision of a developing embryo. By "cooperation ofcompartments," a cone-shaped morphogen distribution can be generated,accounting, e.g., for the circular arrangement of structuresin the fate map of the leg disk of Drosophila. The most distalstructures are formed at the intersection of compartments anddistal transformation occurs whenever cells of all three orfour major compartments are close to each other.     

Genetic variability and chromosome-length polymorphisms of the witches' broom pathogen Crinipellis perniciosa from various plant hosts in South America

Crinipellis perniciosa has been classified into at least four known biotypes associated with members of unrelated plant families. In this study, genetic variability is shown for 27 C (Cacao), 4 S (Solanum), and 7 L biotype (Liana) isolates of C. perniciosa collected from different regions of Brazil and South America. The objective was to investigate the genetic variability of the pathogen in the cacao-producing region of Bahia, Brazil, and elsewhere, through microsatellite analysis, and attempt to identify possible correlations between host specificity and electrophoretic karyotypes. The PCR-banding patterns were found to vary both within and between the different biotypes, and a correlation was established between the PCR-banding patterns and the chromosomal-banding patterns of each isolate. Microsatellite and chromosomal patterns among all of the L and S biotype isolates were distinctly different from the C biotypes analysed. A higher degree of genetic and chromosomal variability was found among C biotype isolates from the Amazon in comparison with C biotype isolates from Bahia, which seems to be comprised of only two main genotypes. This finding has important implications to the current cacao-breeding programme in Brazil.     

Models and Hypotheses

Complex linear appearing structures and networks (e.g. blood vessels, leaf veins, nerves) are formed reproducibly during the development of nearly every organism, but the molecular mechanism leading to such patterns is still unknown. A model is proposed in which a few simple coupled biochemical reactions are able to generate such structures. Among undifferentiated cells, a local peak of differentiation-inducing substance (activator) is formed by autocatalysis and lateral inhibition. The activator peak triggers the differentiation of the cell at that location. Due to changes in metabolism, the differentiated cell repels the activator peak and drives it to a neighbouring cell which then also differentiates. The repulsion between the activator peak and the already differentiated cells forces the activator peak to move ahead of the tip of the extending filament. Long filaments of differentiated cells may be formed, which can split, branch laterally, reconnect with each other and grow towards specific target cells. Partial differential equations describing the mutual interaction of the substances involved were presented and solved with a computer. The resulting patterns show self-regulating properties and other features found in the leaf vascular system, the pattern of tracheae in insect epidermis, and other biological networks.