Evolutionary Conservation of Sequences Directing Chromosome Breakage and Rdna Palindrome Formation in Tetrahymenine Ciliates

Extensive, programmed chromosome breakage occurs during formation of the somatic macronucleus of ciliated protozoa. The cis-acting signal directing breakage has been most rigorously defined in Tetrahymena thermophila, where it consists of a 15-bp DNA sequence known as Cbs, for chromosome breakage sequence. We have identified sequences identical or nearly identical to the T. thermophila Cbs at sites of breakage flanking the germline micronuclear rDNA locus of six additional species of Tetrahymena as well as members of two related genera. Other general features of the breakage site are also conserved, but surprisingly, the orientation and number of copies of Cbs are not always conserved, suggesting the occurrence of germline rearrangement events over evolutionary time. At one end of the T. thermophila micronuclear rDNA locus, a pair of short inverted repeats adjacent to Cbs directs the formation of a giant palindromic molecule. We have examined the corresponding sequences from two other Tetrahymena species. We find the sequence to be partially conserved, as previously implied from analysis of macronuclear rDNA, but of variable length and organization.     

肿瘤坏死因子－α（TNF－α）对常见呼吸道病毒的抑制作用

用人重组肿瘤坏死因子－α（Ｔｕｍｏｒｎｅｃｒｏｓｉｓｆａｃｔｏｒ－α,ＴＮＦ－α）和人天然α干扰素（Ｉｎｔｅｒｆｅｒｏｎ－α－,ＩＦＮ－α）在人胚胎肺纤维母细胞（ＨＥＦ）和Ｈｅｐ－２细胞系上对常见呼吸道病毒所致细胞病变抑制进行比较观察。病毒包括不同型别的腺病毒５株,单疱病毒Ⅰ型（ＨＳＶ－Ｉ）１株,鼻病毒１株,仙台病毒１株,ＶＳＶ１株。结果提示ＴＮＦ－α和ＩＦＮ－α均具有广谱抗病毒活性。ＴＮＦ－α的抑毒作用能被ＴＮＦ－α申抗和ＩＦＮ－β单抗完全去除,被ＩＦＮ－α单抗部分去除ＴＮＦ－α的抗病毒效应。ＴＮＦ－－α中和试验的结果提示：ＴＮＦ抗病毒活性仍为ＩＦＮ－β诱生所介导。     

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.     

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.     

沈阳西部污灌水中有机污染物的分析

沈阳西部污灌水中有机污染物的分析刘海玲,张丽珊,姚家彪,于殿臣,朱岩,可夫,姜萍（中国科学院沈阳应用生态研究所,１１００１５）ＡｎａｌｙｓｉｓｏｆＯｒｇａｎｉｃＰｏｌｌｕｔａｎｔｓｉｎＩｒｒｉｇａｔｅｄｓｅｗａｇｅＩｎＷｅｓｔｅｒｎＳｈｅｎｙａｎｇ．...