Advances in the RNA-directed DNA methylation in plants / 生物工程学报

The RNA-directed DNA Methylation (RdDM) is one type of epigenetic modification which was firstly discovered in plant. RdDM can directly cause DNA modifications of the genome through RNA-DNA interactions. In plant, both of RdDM and mRNA degradation induced by siRNA can silence sequence specific genes through RNA. They play very significant roles in chromosome rearrangement, defence of virus invasion, regulation of gene expression and many processes of plant development. However, the mechanisms of RdDM are still unclear. In this paper the basic characteristics of RdDM were briefly summarized and advances in studies on mechanisms of RdDM were reviewed. These include the kinds of DNA methyltransferases and their functional mechanisms in RdDM, the relationships between DNA methylation and chromatin modification, and important proteins involved in the RdDM process. In plants, RdDM may occur at both the transcriptional and post-transcriptionnal levels, both of which induce gene silencing. Methylation of the target gene promoter correlates with transcriptional gene silencing (TGS) whereas methylation of the coding sequence is associated with post-transcriptional gene silencing (PTGS). RdDM and RNAi all depend on the similar siRNA and enzymes, such as DCL3, RdR2, SDE4 and AGO4. There are at least three kinds of DNA methyltransferases, DRM1/2, MET1 and CMT3, in pants. They can interact with and modifies all cytidines within the DNA regions homologous to RNA sequence. Furthermore, methylation of lysine 9 in Histone H3 can affect the methylation of cytidines.

Forward IMRT planning of nasopharyngeal carcinoma by field aperture shape optimazing based beam direction / 中华放射肿瘤学杂志

Objective To evaluate and summarize a new way of forward intensity modulated radia- tion therapy (IMRT) plan for nasopharyngeal carcinoma with 3Dmulti-leaf collimator (MLC) planning sys- tems is practised routinely in our department.Methods From September 2000 to July 2003 and November 2005 to March 2006,78 patients with nasopharyngeal carcinoma who were treated with eonformal radiothera- py used CT simulation for localizing,then doctors supervised the delineation of the planned tumor volume (PTV),gross tumor volume (GTV) and other sensitive organs on ACQsim workstation,and then sent the CT imagines to ELEKTA Precise Plan by DICOM RT Ethernet.Then,the physicists take over the responsibility of all directions of beam projection according to these organs and PTV shape,and completed the IMRT plan by manual correction making and the optimization of fields or segments shaped with forward 3D planning sys- tem.Results To analyse all the patient's dose distributions taking conformal radiotherapy in our hospital, we found the dose distribution and DVH data excellent,even better than the inverse planning of nasopharyn- geal carcinoma.Conclusions Intensity modulated radiation therapy (IMRT) is an advanced radiotherapy technique.A very good IMRT plan of nasopharyngeal carcinoma by forward planning can be obtained with 3D multiple leaf collimator (MLC) planning system.This planning method is more flexible,but the radia- tion physicists should be very much experienced in professional skill.

The action of S1 nuclease and a cloning strategy for microcircular DNAs / 生物工程学报

S1 nuclease (from Aspergillus oryzae) is a specific enzyme to degrade single stranded DNA or RNA molecules. It has been reported to be able to convert superhelical circular DNA molecules into open circle or linear forms under certain conditions, but this function has not been well explored. In order to use the action of S1 nuclease to linearize circular DNA and develop a novel way of cloning microcircular DNAs, the pUC19 was used to investigate the relationship between the linearization efficiency of S1 nuclease and the amount of enzyme used. By this way the optimal conditions for linearization of circular DNAs by S1 nuclease would be determined. 0.3u to 17u S1 nuclease per 100ng pUC19 DNA was added into a 25 microL system, respectively, to perform the reaction. The effectiveness of enzyme digestion was realized by electrophoresis in a 1.2% agarose gel. The results showed that along with the increase in enzyme amount from 0.3u to 17u a gradual decrease in the superhelical form, a gradual increase in the linear form and then in the circular form was obvious. The conversion from superhelical form to linear and circular form was directly related to the enzyme amount used. A higher proportion of linear DNA molecules was achieved by using 5 to 17u S1 nuclease per 100ng DNA. Besides, electrophoretic mobility of the S1 nuclease-linearized pUC19 was the same as that of the linear form produced by restriction enzyme digestion. According to the result of phiX174 digested by S1 nuclease it has been proposed that the enzyme cleaves first randomly on one site of one strand, thus converting the superhelical molecules into open circle form, and then on the same site of the complementary strand to produce the linear form. Therefore, the S1 nuclease-linearized DNA molecules are intact in the sense of their length and can be used for cloning. The plasmid-like DNA pC3 from cucumber mitochondria is a double stranded circular DNA molecule with about 550bp and the smallest known plasmid-like DNA in eukaryotic mitochondria. Many attempts have been made to linearize the molecule by using restriction enzymes but failed. Therefore, S1 nuclease was used to linearize pC3 based on the results obtained with pUC19. The linearized pC3 DNA molecules formed a very sharp band in a 2.5% agarose gel after electrophoresis. They were then recovered from the gel, added an "A" tail and ligated with T-vector. After transformation into E. coli JM109 cells, the positive clones were, screened by the blue-white selection. The insert was then cut using restriction enzymes EcoRI and Pst I. The result of electrophoresis shows that the electrophoretic mobility of the insert is just the same as that predicted. A 32 P-labled probe was synthesized using pC3 as the template and Southern blot analysis was carried out. The result shows that the inserted DNA is hybridized to the probe, which indicates that the cloned DNA fragment is from pC3. The sequence information of the insert shows that the plasmid-like DNA pC3 was 537bp in length. The nucleotide sequence was deposited in the GenBank (the accession number is AF522195).

Exploring the Antifungal Activity of Bacillus amyloliquefaciens NK10.BAhjaWT / 微生物学通报

Bacillus are well known antibiotic producers. In this study,dozens of Bacillus strains from different sources were screened. Among them,a strain with strong antifungal activity was found. With 16S rDNA test and Biolog assay,this strain was identified to be Bacillus amyloliquefaciens. The fermentation conditions were optimized in small conical flasks. After ammonium sulfate salting out,dialysis,freezing vacuum dehydration,the crude protein extracts were obtained. The thermal stability,pH stability,protease stability,ion stability and antifungal spectrum of this protein were studied further. Scanning electronic microscope was also used to explore the antifungal mechanism.