串联重复序列的物种差异及其生物功能

串联重复序列是指1-200个碱基左右的核心重复单位,以头尾相串联的方式重复多次所组成的重 复序列。它广泛存在于真核生物和一些原核生物的基因组中,并表现出种属、碱基组成等的特异性。在基因组 整体水平上,各种优势的重复序列类型不同。即使在同一重复序列类型内部,不同重复拷贝类别(如AT、AC 等)在基因组中的存在也表现出很大的差异。同时,这些重复序列类型和各重复拷贝类别在同一物种的不同染 色体间,以及基因的编码区和非编码区间也表现种属和碱基组成差异。这些差异显示了重复序列起源和进化的 复杂性,可能涉及到多种机制和因素,并与生物功能密切相关。另外,由于重复序列分析软件和统计标准还存 在算法、重复长度、完美性等问题,需要进一步探讨。此外,串联重复序列的自身进化关系、全基因组水平上 的进化地位、在基因组中的生物功能、重复序列数据库建立和应用研究等,将是今后研究的主要课题。     

中华鲟(Acipenser sinensis)间的长度变异与个体内的长度异质性

用PCR技术扩增中华鲟（Acipensersinensis）线粒体DNA（mtDNA）控制区（D－loop）时,发现中华鲟天然群体内存在个体间和个体内的mtDNA长度变异现象。DNA测序表明,长度变异发生在mtDNAryloop靠近tRANpro的位置,由长约82碱基对（bp）的重复序列串联形成的。由个体内mtDNA长度变异造成的异质性个体比例为57.4％,非异质性（同质性）个体的比例为426％。非异质性个体间的mtDNA的大小也不一样,存在长度变异。在非异质性个体中,有2、3、4、5个串联重复序列形成的4种分子类型的情况,其重复序列出现的频率从高到低的循序是3→2→4→5。在异质性个体中,同一个体由2种不同分子组合的异质体最普通,占77.78％3种不同分子组合的频率次之,占18.520。4种不同分子组合的异质体比例最少,占3．70％。没有发现由5种不同分子组合的异质体。对所有异质体混合分析表明,各种类型的重复序列出现的比例与非异质体的类似,即分子大小（含重复序列数）从高到低的顺序为3→2→4→5→1。对47尾中华鲟的个体内和个体间的遗传多样性指数分析发现,有65．3％遗传变异表现在群体内的个体间,有347％的遗传变异表现在个体内。由mtDNA长度异质性造成的个体内的多样性是中华鳍物种遗传多样性的另一途径。     

Ss‐Rhs1, a secretory Rhs repeat‐containing protein,is required for the virulence of Sclerotinia sclerotiorum

Sclerotinia sclerotiorum is a devastating necrotrophic plant pathogen with a worldwide distribution. Cell wall‐degrading enzymes and oxalic acid are important to the virulence of this pathogen. Here, we report a novel secretory protein, Ss‐Rhs1, which is essential for the virulence of S. sclerotiorum. Ss‐Rhs1 is believed to contain a typical signal peptide at the N‐terminal and eight rearrangement hotspot (Rhs) repeats. Ss‐Rhs1 exhibited a high level of expression at the initial stage of sclerotial development, as well as during the hyphal infection process. Targeted silencing of Ss‐Rhs1 resulted in abnormal colony morphology and reduced virulence on host plants. Microscopic observations indicated that Ss‐Rhs1‐silenced strains exhibited reduced efficiency in compound appressoria formation.     

Assigning DYW-type PPR proteins to RNA editing sites in the funariid mosses Physcomitrella patens and Funaria hygrometrica

The plant‐specific pentatricopeptide repeat (PPR) proteins with variable PPR repeat lengths (PLS‐type) and protein extensions up to the carboxyterminal DYW domain have received attention as specific recognition factors for the C‐to‐U type of RNA editing events in plant organelles. Here, we report a DYW‐protein knockout in the model plant Physcomitrella patens specifically affecting mitochondrial RNA editing positions cox1eU755SL and rps14eU137SL. Assignment of DYW proteins and RNA editing sites might best be corroborated by data from a taxon with a slightly different, yet similarly manageable low number of editing sites and DYW proteins. To this end we investigated the mitochondrial editing status of the related funariid moss Funaria hygrometrica. We find that: (i) Funaria lacks three mitochondrial RNA editing positions present in Physcomitrella, (ii) that F. hygrometrica cDNA sequence data identify nine DYW proteins as clear orthologues of their P. patens counterparts, and (iii) that the ‘missing’ 10th DYW protein in F. hygrometrica is responsible for two mitochondrial editing sites in P. patens lacking in F. hygrometrica (nad3eU230SL, nad4eU272SL). Interestingly, the third site of RNA editing missing in F. hygrometrica (rps14eU137SL) is addressed by the DYW protein characterized here and the presence of its orthologue in F. hygrometrica is explained through its simultaneous action on site cox1eU755SL conserved in both mosses.     

Transfer of small chromosome fragments of Agropyron elongatum to wheat chromosome via asymmetric somatic hybridization

~~Transfer of small chromosome fragments of Agropyron elongatum to wheat chromosome via asymmetric somatic hybridization1 .Dong,Y.C,GenePools of common wheat,Journal of Triticeae CroPs(in Chinese),2000,20(3):78-81. 2 .Wei,Y.M.,Zheng,YL.Zhou,R.H., Detectlon of the rye chro- matin in multisPikelet wheat germplasm 10-A background using fluorescence in situ hybridization(FISH)and RFLP markers,Acta Bot.Sinica(in Chinese),1999,41(7):722-725. 3 .Xiang,E N.,Xia,G M.…     

A naturally occurring point mutation in the 13-mer R repeat affects the <Emphasis Type="Italic">oriC</Emphasis> function of the large chromosome of <Emphasis Type="Italic">Vibrio cholerae</Emphasis> O1 classical biotype

The genome of Vibrio cholerae consists of two circular chromosomes of different sizes. Here, a comparative analysis of the replication origins of the large chromosomes (oriCI_VC) of classical and El Tor biotypes of the pathogen is reported. Extensive nucleotide sequence analyses revealed that the oriCI_VC region has six DnaA boxes instead of the five found in Escherichia coli oriC. The additional DnaA box, designated R_V, was unique in V. cholerae as well as in other members of the family Vibrionaceae. However, R_V was not found to be essential for the autonomous replication function of the 307-bp oriCI_VC minimal region. In contrast to El Tor and the recently evolved V. cholerae O139 strains, the oriCI_VC region of the classical biotype showed only a single base transition (TG) in a highly conserved AT-rich 13-mer R repeat region. From the minichromosome copy number and its transformational efficiency analyses, it appears that the single base substitution in the oriCI_VC of the classical biotype has a significant effect on its replication initiation.     

Mycobacterial PE_PGRS Proteins Contain Calcium-Binding Motifs with Parallel β-roll Folds

The PE_PGRS family of proteins unique to mycobacteria is demonstrated to con- rain multiple calcium-binding and glycine-rich sequence motifs GGXGXD/NXUX. This sequence repeat constitutes a calcium-binding parallel/3-roll or parallel β-helix structure and is found in RTX toxins secreted by many Gram-negative bacteria. It is predicted that the highly homologous PE_PGRS proteins containing multiple copies of the nona-peptide motif could fold into similar calcium-binding structures. The implication of the predicted calcium-binding property of PE_PGRS proteins in the Ught of macrophage-pathogen interaction and pathogenesis is presented.     

Leucine-rich repeat kinase 2 (LRRK2)/PARK8 possesses GTPase activity that is altered in familial Parkinson's disease R1441C/G mutants

Mutations in Leucine-rich repeat kinase 2 (LRRK2) are linked to the most common familial forms and some sporadic forms of Parkinson's disease (PD). The LRRK2 protein contains two well-known functional domains, MAPKKK-like kinase and Rab-like GTPase domains. Emerging evidence shows that LRRK2 contains kinase activity which is enhanced in several PD-associated mutants of LRRK2. However, the GTPase activity of LRRK2 has yet to be formally demonstrated. Here, we produced and purified the epitope-tagged LRRK2 protein from transgenic mouse brain, and showed that purified brain LRRK2 possesses both kinase and GTPase activity as assayed by GTP binding and hydrolysis. The brain LRRK2 is associated with elevated kinase activity in comparison to that from transgenic lung or transfected cultured cells. In transfected cell cultures, we detected GTP hydrolysis activity in full-length as well as in GTPase domain of LRRK2. This result indicates that LRRK2 GTPase can be active independent of LRRK2 kinase activity (while LRRK2 kinase activity requires the presence of LRRK2 GTPase as previously shown). We further found that PD mutation R1441C/G in the GTPase domain causes reduced GTP hydrolysis activity, consistent with the altered enzymatic activity in the mutant LRRK2 carrying PD familial mutations. Therefore, our study shows the biochemical characteristics of brain-specific LRRK2 which is associated with robust kinase and GTPase activity. The distinctive levels of kinase/GTPase activity in brain LRRK2 may help explain LRRK2-associated neuronal functions or dysfunctions in the pathogenesis of PD.     

A new case of partial 14q31.3-qter trisomy due to maternal pericentric inversion

Chromosome 14 is often involved in chromosome rearrangements, although pericentric inversions are rare. Here we report a mother carrying a pericentric inversion of chromosome 14, and her daughter with recombinant chromosome characterized by a partial distal 14q trisomy. Principal clinical findings of the child include facial anomalies, microcephaly, developmental delay, hypotonia and cardiac malformation. Her final karyotype was 46,XX,rec(14)dup(14q)inv(14)(p12q31)mat[20], arr 14q31.3qter(85,427,839–106,356,482)x3. This report brings new data about clinical features of partial 14q trisomy and molecular analysis enables the visualization of genes involved in the segment duplicated.