Spherical protein shell formation from an 11S subunit of bacteriophage f2

An 11S protein component obtained from specific dissociation of bacteriophage f(2) underwent a change in the state of association when dialyzed to pH 4. At low temperatures a dissociation to 5.5S subunits was observed, while at 24 degrees to 34 degrees C a 37S particle was formed. The latter particles have properties which closely resemble those expected for the RNA-free viral capsid.     

水稻基腐细菌Tn5插入突变体库的构建及其致病相关突变体的筛选

采用转座子Tn5插入突变技术,共获得5 261个接合子。通过马铃薯软腐快速筛选和PCR检测验证,获得267个使马铃薯软腐能力丧失或下降的Tn5插入突变体,并测定其在水稻上的致病力和烟草上的过敏性坏死反应(HR)。结果表明:在267个突变体菌株中,对水稻无致病力的有71个,其中在烟草上无HR反应的有59个,产生HR反应的有12个;对水稻致病力下降的有68个,其余突变体菌株对水稻致病力与野生菌株差异不明显。另外,267个突变体菌株中有146个无HR反应,其中有90个对水稻无致病力或者致病力下降。致病力的分析结果表明,获得的突变体是由Tn5插入Dickeya zeae染色体上不同的致病相关基因位点导致的。     

Interspecies conversion of Clostridium botulinum type C to Clostridium novyi type A by bacteriophage

When Clostridium botulinum type C is cured of its prophage it simultaneously ceases to produce toxin. This nontoxigenic culture can then be converted to another toxigenic bacterial species, Clostridium novyi type A or to toxigenic Clostridium botulinum types C or D, by specific bacteriophages. The toxigenicity and type of toxin produced by these cultures depends upon the continued presence of these bacteriophages.     

大豆滞绿(stay-green)突变体诱变后代生理指标及品质分析

为研究大豆滞绿突变体后代中生理指标和品质性状的差异,利用经60 Co-γ诱变的大豆滞绿突变体‘Z-94320’的诱变后代M6为试材,对后代不同种皮色不同子叶色大豆的各时期叶绿素含量、鼓粒期光合作用以及成熟期蛋白质和脂肪含量进行测定并分析。结果表明:滞绿型后代的叶绿素SPAD平均最高可达41.76±0.93,平均变化率可达(12.27±0.70)%,较普通型后代在衰老时期会出现明显的延迟;绿色种皮后代植株叶片的气孔导度会受到抑制,但各类群之间的光合参数无显著差异;滞绿型后代较普通型后代会出现显著的品质提升,且叶绿素变化率与蛋白质含量、脂肪含量呈现极显著的正相关,滞绿型类群中浅绿色种皮、绿色子叶大豆的蛋白质含量和脂肪含量比绿色种皮、子叶大豆分别高出(44.35±0.16)和(21.57±0.03)g/100g,因此,品质更优。     

批量筛选水稻T-DNA插入突变体库获得生殖发育相关突变体

针对花器官形态和种子发育突变表型对大型水稻T-DNA插入突变体库进行筛选,获得了大量突变体信息及材料,在9 760个突变体家系中筛选得到177个花器官形态和数量异常的突变家系,突变频率为1.81%;对9 760个家系中的3 432个家系筛选得到179个种子发育缺陷的突变家系,突变频率为5.22%。对所获得的270个突变家系进行了T-DNA插入的阳性检测,阳性率为64.8%。利用公共数据库RMD(Rice MutantDatabase,RMD)给定的侧翼序列,鉴定了其中1个结实率较低的突变体家系,表明其突变表型和T-DNA插入共分离,为深入研究该基因的功能提供了重要的遗传材料。     

Recombination in bacteriophage T4: a mechanism

Genetic recombination between rIl mutants of T4 bacteriophage grown in Escherichia coli can occur under conditions where DNA synthesis is strongly inhibited by 5-fluorodeoxyuridine. The small amount of DNA synthesized under these conditions cannot account for the observed frequency of recombinants. The major mechanism of recombination in this system is a process of breakage and rejoining.     

Replication of the RNA of Bacteriophage f2

Events occurring after infection of bacteria with wild-type and a temperature-sensitive mutant phage indicate that there are two enzymatic activities necessary to replicate phage RNA. One converts single strands into double strands, while the other uses double strands to svnthesize viral RNA. The mutant is deficient in the first activity, probably because the mutation is in the gene specifying the requisite enzyme. On the basis of these and other results, a model is presented for the replication of phage RNA.     

Prophage S2 mutants in Haemophilus influenzae: a technique for their production and isolation

A procedure utilizing nitrosoguanidine has been developed to produce defective and temperature-sensitive mutants of prophage (S2) in lysogenic Haemophilus influenzae. The system should be generally applicable to all temperate phage systems. At saturating concentrations of phage DNA, more than 25 percent of recipient mutant lysogenic bacteria can be transformed to the wild type.     

Mosaic mutants: absence in a eucaryotic organism

Exposure of procaryotic and eucaryotic cells to mutagenic agents generally gives both complete mutants and mosaic mutants. Irradiation of the eucaryotic multicellular alga Ulva mutabilis with ultraviolet light has given exclusively complete mutants.     

Cell Lysis: Another Function of the Coat Protein of the Bacteriophage f2

Evidence is presented that the coat protein of bacteriophage f2 causes the lysis of infected Escherichia coli. To lyse bacteria, the coat protein produced must be of the quality to produce phage particles, although it need not be produced in amounts sufficient to give a large yield of particles. Mutants that are blocked in coat-protein synthesis, or that direct the synthesis of an imperfect coat protein, do not lyse their host bacteria. In addition to its obvious structural role and its postulated regulatory role, another, perhaps enzymatic, role has been found for the coat protein of the phage f2.     

西瓜专化型尖孢镰刀菌FonSIX6缺失突变体的构建

病原菌和植物相互作用时分泌效应蛋白（effectors）抑制植物的防卫反应。枯萎病是由尖孢镰刀菌引起的真菌病害,尖孢镰刀菌和寄主相互作用时分泌几个特定的富含半胱氨酸的小分子量蛋白（15.8～29.9 kD）进入木质部启动致病力,称为SIX（secreted in xylem）蛋白,其中,SIX6蛋白是一个效应蛋白。西瓜枯萎病是由西瓜专化型尖孢镰刀菌（Fusarium oxysporum f. sp.Niveurn,Fon）引起的真菌病害。为了明确FonSIX6在侵染西瓜时的作用,克隆了该基因的上下游序列,以潮霉素为筛选标记构建了该基因的缺失突变体载体pDH\|SIX6;将构建好的基因缺失载体转入农杆菌AGL\|1中,通过农杆菌介导的遗传转化和转化子的筛选获得了FonSIX6基因的缺失突变体。     

大豆低植酸突变体Gm-lpa-ZC-2的精细定位

降低大豆植酸含量对于改善大豆营养品质极其重要。通过诱变的方法筛选到大豆低植酸突变体Gm-lpa-ZC-2,经典遗传学分析表明：其突变性状由隐性单基因所控制,并被定位在大豆连锁群B2上。试验在大豆低植酸突变体Gm-lpa-ZC-2初步定位的基础上,通过构建较大的遗传群体,运用生物信息学发展新的连锁标记,结合大豆基因组学和传统定位的方法,进行突变基因的精确定位。结果表明：位于大豆B2连锁群上的Gm-lpa-ZC-2突变基因,与连锁标记Satt168和Satt416的遗传距离远大于初步定位的结果,为18.2 cM;在此基础上,利用大豆基因组序列信息,在Satt168标记的上游序列与目的基因之间的染色体片段,4 900～8 200 kb的区域中,发掘到9对在遗传群体亲本间具有多态性的SSR引物;其中SSR位点psm lpa-224,psm lpa-225和psm lpa-226与目的基因的距离仅为0.8 cM,实现了突变基因的精细定位。     

冰岛硫化叶菌xpb基因缺失突变体的构建及遗传学分析

为在体内研究古菌核苷酸切除修复(nucleotide excision repair,NER)机制,利用基因敲除的方法,对泉古菌核苷酸切除修复机制进行研究,构建了冰岛硫化叶菌编码真核生物NER解旋酶XPB同源蛋白的基因xpb1和xpb2单缺失突变体,从而在体内分析xpb1和xpb2基因的功能。结果表明:基因xpb1或xpb2不是冰岛硫化叶菌存活的必需基因。表型分析发现,xpb1和xpb2基因单缺失突变体相较野生型菌株REY15A,对DNA损伤试剂4-NQO 4-硝基喹啉-1-氧化物(4-nitroquinoline 1-oxide,4-NQO)分别表现出轻微敏感性和不敏感性,暗示NER解旋酶功能在冰岛硫化叶菌体内存在多重冗余。     

航天诱变凤仙花SP2代叶片形状变异分析

对航天诱变凤仙花SP 2代若干单株的叶片长度和宽度进行了统计分析,对试验数据进行了柯尔莫哥罗夫-斯米尔诺夫检验,计算了样本的列文统计量,并采用Spss 11.5统计分析软件检验了基本假设的满足条件,进行了独立样本t检验。结果表明,航天诱变凤仙花SP 2代植株的叶片存在变异;试验组SP 2代植株的叶片长度与对照组相比差异显著,叶片宽度差异不显著。     

西瓜枯萎病菌(Fusarium oxysporum f.sp.niveum)营养体亲和群研究

从浙江各地、江苏南部和上海等地采集的西瓜枯萎病株和其他瓜类植株上,分离纯化尖孢镰孢霉(Fusarium oxysporum)菌种23个(每个菌种来自一个植株样本).接种试验表明:酉瓜植株上分离的19个菌种,有16个对长蜜、新红宝和圳宝等3个酉瓜品种表现为致病性,而其他菌种表现为非致病性.所有23个菌种均获得抗氯酸盐的硝酸盐营养突变株(nit mutant).根据来自同一菌种nit突变株的营养体亲和性与突变类型鉴定,选择3个西瓜致病菌的Nit M类型突变株(W 024～5,W 072～4和W 014～9)为营养体亲和性测试株.各菌种上获得的nit突变株分别与测试株作营养体亲和性配对反应,23个菌种可划分成8个营养体亲和群(VCG)和1个营养体自身非亲和类型.16个西瓜致病菌中,除一个为营养体自身非亲和类型外,其余均属同一亲和群(M1001),而与西瓜非致病菌不存在营养体亲和反应.由此显示:营养体亲和群与西瓜枯萎病菌存在相关性,而与地理分布无关.     

Mini-mouse: disruption of the pygmy locus in a transgenic insertional mutant

A founder transgenic mouse harbored two different integration patterns of a transgene at the same locus, each of which gave rise to a similar autosomal recessive mutation. Mice of the mutant phenotype were of small stature but had normal levels of growth hormone. The disrupted locus was cloned, and a genetic and molecular analysis showed that the insertional mutants were allelic to a spontaneous mutant, pygmy. The mice should be a useful model for the growth hormone-resistant human dwarf syndromes and could lead to a greater understanding of the pathways involved in growth and development.