Nucleotide sequence of the yeast plasmid

The nucleotide sequence of the yeast DNA plasmid (2 mu circle) from Saccharomyces cerevisiae strain A364A D5 has been determined. The plasmid contains 6,318 base pairs, including two identical inverted repeats of 599 base pairs. Possible functions are suggested, and attributes of an improved vector for cloning foreign DNAs in yeast are discussed.     

Increased viral pathogenicity after insertion of a 28S ribosomal RNA sequence into the haemagglutinin gene of an influenza virus

The haemagglutinin glycoprotein HA of influenza viruses is responsible for the attachment of the virus to neuraminic acid-containing receptors at the cell surface and subsequent penetration by triggering fusion of the viral envelope with cellular membranes. To express full activity of the newly synthesized precursor, HA has to be modified by post-translational proteolytic cleavage into the polypeptides HA1 and HA2 by cellular enzymes. If proteases suitable for cleavage are not present in the host cell, the resulting virus particles are non-infectious. During adaptation of the apathogenic influenza virus A/turkey/Oregon/71 to chicken embryo cells, which are not permissive for HA cleavage, we obtained an infectious virus variant with increased pathogenicity. Sequence analysis revealed that during adaptation 54 nucleotides were inserted into the HA gene; their sequence corresponds to a region of the 28S ribosomal RNA. This insertion is probably responsible for increased cleavability of HA, as well as for infectivity and pathogenicity of the adapted virus.     

Recovery of 16S ribosomal RNA gene fragments from ancient halite

During the last decade, sensitive techniques for detecting DNA have been successfully applied to archaeological and other samples that were a few hundred to a few thousand years old. Nevertheless, there is still controversy and doubt over claims of exceptionally ancient DNA. Additional accounts stretching back nearly a century suggest that microorganisms may survive over geological time in evaporite deposits. There is, however, often doubt over the age relationship between evaporite formation and the incorporation of microorganisms. Here, we have used petrographic and geochemical techniques (laser ablation microprobe inductively coupled plasma mass spectrometry) to verify the estimated geological age of halite (NaCl) evaporite samples. Fragments of 16S ribosomal RNA genes were detected by polymerase chain reaction amplification of DNA extracted from halite samples ranging in age from 11 to 425 Myr (millions of years). Haloarchaeal 16S rDNA amplicons were present in one sample (11 16 Myr), whereas other samples (65 425 Myr) yielded only bacterial 16S rDNA amplicons. Terminal restriction fragment length polymorphism analyses indicate complex and different populations of microorganisms or their free DNA in ancient halites of different ages.     

Placement of protein and RNA structures into a 5 A-resolution map of the 50S ribosomal subunit.

We have calculated at 5.0 A resolution an electron-density map of the large 50S ribosomal subunit from the bacterium Haloarcula marismortui by using phases derived from four heavy-atom derivatives, intercrystal density averaging and density-modification procedures. More than 300 base pairs of A-form RNA duplex have been fitted into this map, as have regions of non-A-form duplex, single-stranded segments and tetraloops. The long rods of RNA crisscrossing the subunit arise from the stacking of short, separate double helices, not all of which are A-form, and in many places proteins crosslink two or more of these rods. The polypeptide exit channel was marked by tungsten cluster compounds bound in one heavy-atom-derivatized crystal. We have determined the structure of the translation-factor-binding centre by fitting the crystal structures of the ribosomal proteins L6, L11 and L14, the sarcin-ricin loop RNA, and the RNA sequence that binds L11 into the electron density. We can position either elongation factor G or elongation factor Tu complexed with an aminoacylated transfer RNA and GTP onto the factor-binding centre in a manner that is consistent with results from biochemical and electron microscopy studies.     

Nucleotide sequence of the rat skeletal muscle actin gene

The actins constitute a family of highly conserved proteins found in all eukaryotic cells. Their conservation through a very wide range of taxonomic groups and the existence of tissue-specific isoforms make the actin genes very interesting for the study of the evolution of genes and their controlling elements. On the basis of amino acid sequence data, at least six different mammalian actins have been identified (skeletal muscle, cardiac muscle, two smooth muscle actins and the cytoplasmic beta- and gamma-actins). Rat spleen DNA digested by the EcoRI restriction enzyme contains at least 12 different fragments with actin-like sequences but only one which hybridized, in very stringent conditions, with the skeletal muscle cloned cDNA probe. Here we describe the sequence of the actin gene in that fragment. The nucleotide sequence codes for two amino acids, Met-Cys, preceding the known N-terminal Asp of the mature protein. There are five small introns in the coding region and a large intron in the 5'-untranslated region. Comparison of the structure of the rat skeletal muscle actin gene with available data on actin genes from other organisms shows that while the sequenced actin genes from Drosophila and yeast have introns at different locations, introns located at codons specifying amino acids 41, 121, 204 and 267 have been preserved at least from the echinoderm to the vertebrates. A similar analysis has been done by Davidson. An intron at codon 150 is common to a plant actin gene and the skeletal muscle acting gene.     

BmNPV半胱氨酸蛋白酶基因的核苷酸序列研究

对家蚕核型多角体病毒苏州株（BmNPVsu）半胺氨酸蛋白酶基因（CP）的序列分析表明，该基因读码框为972个核苷酸，编码323个氨。同源性分析表明，BmNPVsu CP的氨基酸序列与不同来源的木瓜蛋白酶超家庭的CP具有较高的同源性，特别与Trpanosomabrucei的CP具有较高的一致性，达32％。在组织蛋白酶B、H、L、S以及木瓜蛋白酶的36个保守氨基酸残基中有31种出现在BmNPUsu的CP中，BmNPVsuCP同其他杆状病毒CP一样，可看作木瓜蛋白酶超家庭成员。