旋扭山绿豆根瘤菌MXDI6菌株氢酶诱导表达

在自生异养条件下,旋扭山绿豆根瘤菌ＭＸＤＩ６菌株的氢酶诱导表达受气相、ｐＨ值、镍等因子影响：氢酶表达的最适氧浓度为４％,最适氢浓度为１５％,二氧化碳没有明显影响;氢酶表达的ｐＨ值以５．０—６．０为宜;０．５μｍｏｌ／ＬＮｉＣｌ２明显促进吸氢活性,但镍浓度大于１μｍｏｌ／Ｌ则抑制吸氢活性．     

Ultrastructure of the spermatozoa and eggs of the ocean pout (Macrozoarces americanus L.), an internally fertilizing marine fish

Ultrastructure of sperm and eggs of the ocean pout (Macrozoarces americanus L.), an internally fertilizing marine teleost, was examined by scanning and transmission electron microscopy. The results showed that the sperm do not have an acrosome but have a very long mid-piece (one to two times the sperm head length) containing numerous well-developed elongated mitochondria. The sperm also have two tails (is biflagellate) each consisting of nine peripheral and one central pair (9 ± 2) of microtubules. This long mid-piece and the biflagellate nature of the sperm appear to be associated with the long life-span of the sperm and with sperm dispersal in the ovary to fertilize the eggs internally. The ocean pout eggs are enveloped by a porous chorionic membrane similar to that found in other teleosts but have two micropyles, a condition likely related to a mechanism of egg fertilization which increases the egg fertlity in the presence of low sperm numbers. Following insemination, some biochemically undefined excretions appeared on the surface of fertilized eggs and led to the acquisition of adherent capability of the eggs which formed a tightly associated egg mass in sea water. © 1995 wiley-Liss, Inc.     

An rRNA variable region has an evolutionarily conserved essential role despite sequence divergence.

Regions extremely variable in size and sequence occur at conserved locations in eukaryotic rRNAs. The functional importance of one such region was determined by gene reconstruction and replacement in Tetrahymena thermophila. Deletion of the D8 region of the large-subunit rRNA inactivates T. thermophila rRNA genes (rDNA): transformants containing only this type of rDNA are unable to grow. Replacement with an unrelated sequence of similar size or a variable region from a different position in the rRNA also inactivated the rDNA. Mutant rRNAs resulting from such constructs were present only in precursor forms, suggesting that these rRNAs are deficient in either processing or stabilization of the mature form. Replacement with D8 regions from three other organisms restored function, even though the sequences are very different. Thus, these D8 regions share an essential functional feature that is not reflected in their primary sequences. Similar tertiary structures may be the quality these sequences share that allows them to function interchangeably.     

Detection of circular excised DNA deletion elements in Tetrahymena thermophila during development.

Extensive programmed DNA deletion occurs in ciliates during development. In this study we examine the excised forms of two previously characterized deletion elements, the R- and M-element, in Tetrahymena. Using divergently oriented primers in polymerase chain reactions we have detected the junctions formed by joining the two ends of these elements, providing evidence for the presence of circular excised forms. These circular forms were detected in developing macronuclear DNA from 12-24 h after mating began, but not in micronuclear or whole cell DNA of vegetative cells. They are present at very low abundance, detectable after PCR only through hybridization with specific probes. Sequence analysis shows that the circle junctions occur at or very near the known ends of the elements. There is sequence microheterogeneity in these junctions, which does not support a simple reciprocal exchange model for DNA deletion. A model involving staggered cuts and variable mismatch repair is proposed to explain these results. This model also explains the sequence microheterogeneity previously detected among the junction sequences retained in the macronuclear chromosome.     

Mapping of a Magnaporthe grisea locus affecting rice (Oryza sativa) cultivar specificity

Magnaporthe grisea causes rice blast, the most important fungal disease of rice. The segregation of genes controlling virulence of M. grisea on rice was studied to establish the genetic basis of cultivar specificity in this host-parasite interaction. Full-sib progeny and parent isolates Guy11 and 2539 of M. grisea were inoculated onto rice (Oryza sativa) cultivar CO39 and five near-isogenic lines (NILs) of CO39. Each NIL contained a different single gene affecting resistance to specific isolates of M. grisea. No differential interactions between NILs and progeny or parents were observed; parents and progeny pathogenic on CO39 were pathogenic on all five NILs. Segregation ratios of 101 full-sib progeny, 117 progeny from full-sib parents, and 109 backcross progeny, indicated a common single gene affecting pathogenicity on CO39 and the five NILs. A subset of the above 327 isolates (43 fullsib progeny, 37 progeny from full-sib parents, and 32 backcross progeny) were inoculated onto rice cultivar 51583; all were pathogenic, indicating that cultivar specificity to CO39 was segregating in this population of isolates. The locus controlling cultivar specificity, named avrCO39, was mapped to chromosome 1 using a subset of the progeny previously used to construct an RFLP map of M. grisea. The closest reported RFLP markers were 11.8 (estimated 260 kb) and 17.2 cM (estimated 380 kb) away and provide starting points on either side of the locus for a chromosome walk to clone the locus.     

Requirement of the Pr55gag precursor for incorporation of the Vpr product into human immunodeficiency virus type 1 viral particles.

The human immunodeficiency virus type 1 (HIV-1) particles consists of two molecules of genomic RNA as well as molecules originating from gag, pol, and env products, all synthesized as precursor proteins. The 96-amino-acid Vpr protein, the only virion-associated HIV-1 regulatory protein, is not part of the virus polyprotein precursors, and its incorporation into virus particles must occur by way of an interaction with a component normally found in virions. To investigate the mechanism of incorporation of Vpr into the HIV-1 virion, Vpr- proviral DNA constructs harboring mutations or deletions in specific virion-associated gene products were cotransfected with Vpr expressor plasmids in COS cells. Virus released from the transfected cells was tested for the presence of Vpr by immunoprecipitation with Vpr-specific antibodies. The results of these experiments show that Vpr is trans-incorporated into virions but at a lower efficiency than when Vpr is expressed from a proviral construct. The minimal viral genetic information necessary for Vpr incorporation was a deleted provirus encoding only the pr55gag polyprotein precursor. Incorporation of Vpr requires the expression but not the processing of gag products and is independent of pol and env expression. Direct interaction of Vpr with the Pr55gag precursor protein was demonstrated by coprecipitation experiments with gag product-specific antibodies. Overall, these results indicate that HIV-1 Vpr is incorporated into the nascent virion through an interaction with the Gag precursor polyprotein and demonstrate a novel mechanism by which viral protein can be incorporated into virus particles.     

Nucleocapsid-glycoprotein interactions required for assembly of alphaviruses.

We have studied interactions between nucleocapsids and glycoproteins required for budding of alphaviruses, using Ross River virus-Sindbis virus chimeras in which the nucleocapsid protein is derived from one virus and the envelope glycoproteins are derived from the second virus. A virus containing the Ross River virus genome in which the capsid protein had been replaced with that from Sindbis virus was almost nonviable. Nucleocapsids formed in normal numbers in the infected cell, but very little virus was released from the cell. There are 11 amino acid differences between Ross River virus and Sindbis virus in their 33-residue E2 cytoplasmic domains. Site-specific mutagenesis was used to change 9 of these 11 amino acids in the chimera from the Ross River virus to the Sindbis virus sequence in an attempt to adapt the E2 of the chimera to the nucleocapsid. The resulting mutant chimera grew 4 orders of magnitude better than the parental chimeric virus. This finding provides direct evidence for a sequence-specific interaction between the nucleocapsid and the E2 cytoplasmic domain during virus budding. The mutated chimeric virus readily gave rise to large-plaque variants that grew almost as well as Ross River virus, suggesting that additional single amino acid substitutions in the structural proteins can further enhance the interactions between the disparate capsid and the glycoproteins. Unexpectedly, change of E2 residue 394 from lysine (Ross River virus) to glutamic acid (Sindbis virus) was deleterious for the chimera, suggesting that in addition to its role in nucleocapsid-E2 interactions, the N-terminal part of the E2 cytoplasmic domain may be involved in glycoprotein-glycoprotein interactions required to assemble the glycoprotein spikes. The reciprocal chimera, Sindbis virus containing the Ross River virus capsid, also grew poorly. Suppressor mutations arose readily in this chimera, producing a virus that grew moderately well and that formed larger plaques.     

陕西省常见蜜源植物花粉形态的研究

运用扫描电子显微镜,对陕西省境内３０种常见蜜源植物的花粉粒进行了观察研究,描述了花粉粒的大小、萌发孔类型及其表面纹饰等形态特征。结果表明：绝大多数种的蜜源植物,其花粉粒的形态特征明显不同。本文还就花粉粒形态特征,在鉴定蜜源植物花粉的属种,确定蜂蜜的产地、评价蜂蜜的品质等方面进行了探讨。