Sex chromosome pairing and sex chromatin bodies in W-Z translocation strains of Ephestia kuehniella (Lepidoptera).

Structure and pairing behavior of sex chromosomes in females of four T(W;Z) lines of the Mediterranean flour moth, Ephestia kuehniella, were investigated using light and electron microscopic techniques and compared with the wild type. In light microscopic preparations of pachytene oocytes of wild-type females, the WZ bivalent stands out by its heterochromatic W chromosome strand. In T(W;Z) females, the part of the Z chromosome that was translated onto the W chromosome was demonstrated as a distal segment of the neo-W chromosome, displaying a characteristic non-W chromosomal chromomere-interchromomere pattern. This segment is homologously paired with the corresponding part of a complete Z chromosome. In contrast with the single ball of heterochromatic W chromatin in highly polyploid somatic nuclei of wild-type females, the translocation causes the formation of deformed or fragmented W chromatin bodies, probably owing to opposing tendencies of the Z and W chromosomal parts of the neo-W. In electron microscopic preparations of microspread nuclei, sex chromosome bivalents were identified by the remnants of electron-dense heterochromatin tangles decorating the W chromosome axis, by the different lengths of the Z and W chromosome axes, and by incomplete pairing. No heterochromatin tangles were attached to the translocated segment of the Z chromosome at one end of the neo-W chromosome. Because of the homologous pairing between the translocation and the structurally normal Z chromosome, pairing affinity of sex chromosomes in T(W;Z) females is significantly improved. Specific differences observed among T(W;Z)1-4 translocations are probably due to the different lengths of the translocated segments.     

The Intercellular Distribution of Mutations Induced in Oocytes of DROSOPHILA MELANOGASTER by Chemical and Physical Mutagens

When females of Drosophila melanogaster are treated with chemical or physical mutagens, not only in one but also in both of the two homologous X chromosomes of a given oocyte, a recessive sex-linked lethal mutation may be induced. A method is described that discriminates between such "single" and "double mutations". A theory is developed to show how a comparison between the expected and the observed frequency of double mutations yields an indication of the intercellular distribution (random or nonrandom) of recessive lethal mutations induced by mutagenic agents in oocytes and, consequently, of the distribution (homogeneous or nonhomogeneous) of those agents.--Three agents were tested: FUdR (12.5, 50.5 and 81.0 micrograms/ml), mitomycin C (130.0 micrograms/ml) and X rays (2000 R, 150 kV). After FUdR feeding, no increase in the mutation frequency usually observed in D. melanogaster without mutagenic treatment was obtained (u = 0.13%, namely three single mutations among 2332 chromosomes tested). After mitomycin C feeding, 104 single and three double mutations were obtained. All of the 50 mutations observed after X irradiation were single mutations. The results obtained in the mitomycin C and radiation experiments favor the assumption of a random intercellular distribution of recessive lethal mutations induced by these two agents in oocytes of D. melanogaster. Reasons are discussed why for other types of mutagenic agents nonrandom distributions may be observed with our technique.     

Opposite sex-specific effects of Wolbachia and interference with the sex determination of its host Ostrinia scapulalis

In the adzuki bean borer, Ostrinia scapulalis, the sex ratio in most progenies is 1 : 1. Females from Wolbachia-infected matrilines, however, give rise to all-female broods when infected and to all-male broods when cured of the infection. These observations had been interpreted as Wolbachia-induced feminization of genetic males into functional females. Here, we show that the interpretation is incorrect. Females from both lines have a female karyotype with a WZ sex-chromosome constitution while males are ZZ. At the time of hatching from eggs, WZ and ZZ individuals are present at a 1 : 1 ratio in broods from uninfected, infected and cured females. In broods from Wolbachia-infected females, ZZ individuals die during larval development, whereas in those from cured females, WZ individuals die. Hence, development of ZZ individuals is impaired by Wolbachia but development of WZ females may require the presence of Wolbachia in infected matrilines. Sexual mosaics generated (i) by transfection of uninfected eggs and (ii) by tetracycline treatment of Wolbachia-infected mothers prior to oviposition were ZZ in all tissues, including typically female organs. We conclude that: (i) Wolbachia acts by manipulating the sex determination of its host; and (ii) although sexual mosaics can survive, development of a normal female is incompatible with a ZZ genotype.     

TROMB, a new retrotransposon of the gypsy-Ty3 group from the fly Megaselia scalaris

We describe TROMB, a new LTR retrotransposon, from the phorid fly Megaselia scalaris. Three full-length copies (4226, 4160 and 4129bp) and a truncated one (319bp) have been isolated. The target site consensus is TATAT, with a 4bp target site duplication TATA. The LTRs are short (142bp) and contain a TATA-box and a polyadenylation signal. The isolated copies are degenerate to different degrees and presumably inactive. The polyprotein coding sequence contains scattered stop codons and deletions/insertions at non-homologous positions. The consensus sequence among the three full-length copies, however, has an uninterrupted open reading frame and, presumably, represents the original sequence of the active element. Southern hybridization experiments showed TROMB to be present at a low copy number in two wild-type strains of M. scalaris and absent in a related species, M. abdita. The order of domains in the polyprotein coding region, the target site specificity for AT-rich sequences, and the protein sequence similarity to blastopia, mdg3 and micropia place TROMB in the gypsy-Ty3 group of LTR retrotransposons.     

Ribosomal protein L2 is involved in the association of the ribosomal subunits, tRNA binding to A and P sites and peptidyl transfer

Ribosomal proteins L2, L3 and L4, together with the 23S RNA, are the main candidates for catalyzing peptide bond formation on the 50S subunit. That L2 is evolutionarily highly conserved led us to perform a thorough functional analysis with reconstituted 50S particles either lacking L2 or harboring a mutated L2. L2 does not play a dominant role in the assembly of the 50S subunit or in the fixation of the 3'-ends of the tRNAs at the peptidyl-transferase center. However, it is absolutely required for the association of 30S and 50S subunits and is strongly involved in tRNA binding to both A and P sites, possibly at the elbow region of the tRNAs. Furthermore, while the conserved histidyl residue 229 is extremely important for peptidyl-transferase activity, it is apparently not involved in other measured functions. None of the other mutagenized amino acids (H14, D83, S177, D228, H231) showed this strong and exclusive participation in peptide bond formation. These results are used to examine critically the proposed direct involvement of His229 in catalysis of peptide synthesis.     

Cryo-electron microscopic localization of protein L7/L12 within the Escherichia coli 70 S ribosome by difference mapping and Nanogold labeling

The Escherichia coli ribosomal protein L7/L12 is central to the translocation step of translation, and it is known to be flexible under some conditions. The assignment of electron density to L7/L12 was not possible in the recent 2.4 A resolution x-ray crystallographic structure (Ban, N., Nissen, P., Hansen, J., Moore, P. B., and Steitz, T. A. (2000) Science 289, 905-920). We have localized the two dimers of L7/L12 within the structure of the 70 S ribosome using two reconstitution approaches together with cryo-electron microscopy and single particle reconstruction. First, the structures were determined for ribosomal cores from which protein L7/L12 had been removed by treatment with NH(4)Cl and ethanol and for reconstituted ribosomes in which purified L7/L12 had been restored to core particles. Difference mapping revealed that the reconstituted ribosomes had additional density within the L7/L12 shoulder next to protein L11. Second, ribosomes were reconstituted using an L7/L12 variant in which a single cysteine at position 89 in the C-terminal domain was modified with Nanogold (Nanoprobes, Inc.), a 14 A gold derivative. The reconstruction from cryo-electron microscopy images and difference mapping placed the gold at four interfacial positions. The finding of multiple sites for the C-terminal domain of L7/L12 suggests that the conformation of this protein may change during the steps of elongation and translocation.     

A jumping sex determining factor in the flyMegaselia scalaris

To test earlier reports on changes of the sex determining linkage group inMegaselia scalaris, we used a combination of a cytogenetic and a phenotypic marker in a laboratory strain as a detection system for rare cases in which linkage of the marker and the Y chromosome was disrupted. From some of the exceptional males detected in this system we established strains with a different chromosome pair acting as the sex chromosome pair. Cytogenetic analysis, crossbreeding tests with a phenotypic marker and DNA blot hybridization with cloned DNA probes indicated that an epistatic male determining factor had moved to one of the former autosomes at a frequency of at least 0.06%.     

香菇的学名及其在当代真菌分类中的位置

本文综述了香菇(Lentinula edodes)的分类历史,确认其在蘑菇目(Agaricales)Tricholomataceae科下的分类地位,并证实了它与多孔菌目(Poriales)Lentinaceae科的Lentinus属没有联系。根据《真菌、地衣汉语学名命名法规》,作者讨论了译为“香菇属”的Lentinus和“小香菇属”的Lentinellus两属的汉语学名问题,提出Lentinus的汉语学名应订正为“韧伞属”,Lentinellus为“螺壳菌属”。香菇所在的Lentinula属的汉语学名建议为“木菇属”。