Frameshift Suppression by thyA Mutants of ESCHERICHIA COLI K-12

We have extended our previous study on the suppression of frameshift mutants by Escherichia coli thyA mutants by assaying suppression of 15 rIIB frameshift mutants of bacteriophage T4 on one of our suppressing thyA mutant strains. The majority of insertion mutants were suppressible, whereas none of the deletion mutants tested was suppressible. Frameshift suppression could be inhibited by adding thymidine to the assay medium, but was not affected by the presence of a restrictive rpsL mutation in the host strain. We suggest that the frameshift suppression event occurs at a nonsense codon generated by the frameshift mutation.     

An antisuppressor mutation of Schizosaccharomyces pombe affects the post-transcriptional modification of the "wobble" base in the anticodon of tRNAs

The screening of antisuppressor mutants of the yeast Schizosaccharomyces pombe has been successfully accomplished with high resolution liquid chromatographic methods for the analysis of tRNA nucleosides. Antisuppressor mutations reduce or abolish the function of nonsense suppressor-tRNAs or other informational suppressors. Nonradioactive or 35S-labeled unfractionated tRNA from various strains was digested to nucleosides and analyzed by high performance liquid chromatography. The mutant sin3 has lost the nucleoside 5-(methoxycarbonylmethyl)-2-thiouridine from its tRNA in comparison to parental strains. In eukaryotes this nucleoside is found at the first position of the anticodon (wobble position) in several isoacceptor tRNAs that preferentially recognize codons ending with adenosine. The sin3 mutation reduces the efficiency of UGA and UAA suppressor tRNASer and suppressor tRNALeu. The genetic cosegregation of modification loss, antisuppressor phenotype, and a change in cell size is demonstrated. This indicates that a single mutation in the structural gene for a tRNA modification enzyme causes the three different phenotypes.     

Isolation of a human anti-haemophilic factor IX cDNA clone using a unique 52-base synthetic oligonucleotide probe deduced from the amino acid sequence of bovine factor IX

A unique 52mer oligonucleotide deduced from the amino acid sequence of bovine Factor IX was synthesized and used as a probe to screen a human liver cDNA bank. The Factor IX clone isolated shows 5 differences in nucleotide and deduced amino acid sequence as compared to a previously isolated clone. In addition, precisely one codon has been deleted.     

Adenosine triphosphate content of Mycobacterium leprae by percoll buoyant density centrifugation.

Thirty nine untreated patients of bacilliferous leprosy with a mean bacteriological index of 4.8 and morphological index of 1.3% formed the study group. Adenosine triphosphate assay was carried out by (i) enzyme treatment method in 18 patients and (ii) percoll buoyant density gradient method in 21 patients. ATP content obtained by percoll buoyant density gradient method was significantly higher than that obtained by enzyme treatment method. Percoll buoyant density centrifugation for purification and isolation of bacilli from human leproma is simplier, quicker and can serve as an alternate method of enzyme treatment.     

Induction of polysubstrate monooxygenase and aflatoxin production by phenobarbitone in Aspergillus parasiticus NRRL 3240

The presence of the components of polysubstrate monooxygenase (PSMO) activity, viz., cytochrome P-450 and NADPH cytochrome P-450 reductase has been established for the first time in the microsomes of $\text{Aspergillus parasiticus}$. The microsomes were able to metabolize benzphetamine. NADPH cytochrome P-450 reductase, benzphetamine metabolism and aflatoxin production was increased by the presence of phenobarbitone (PB, 2mg/ml) in the medium. These results demonstrate that induction of PSMO activity could be a prerequisite for increased production of aflatoxins, since hydroxylation of intermediates is an obligatory step in aflatoxin biosynthesis.     

Silica gel: an improved support for the solid-phase phosphotriester synthesis of oligonucleotides.

The phosphotriester method for the stepwise synthesis of deoxyoligonucleotides has been employed using HPLC-grade silica gel (Porasil B) as the solid support. The procedure results in a convenient flow-through system for the synthesis of oligomers where all the reaction steps including the zinc bromide method of detritylation are compatible with the selected support. Deoxyoligonucleotides of 25-30 nucleotides in length can be synthesized in high yields utilising stable phosphotriester intermediates. Ease of handling of the solid support allows convenient synthesis of mixed oligonucleotide sequences.     

The nucleotide sequence of the major glutamate transfer RNA from Schizosaccharomyces pombe.

The nucleotide sequence of glutamate tRNA1 from Schizosaccharomyces pombe was determined to be pU-C-C-G-U-U-G-U-m1G-G-U-C-C-A-A-C-G-G-C-D-A-G-G-A-U-U-C-G-U-C-G-C-U-U-U*-C-A-C-C-G-A-C-G-G-G-A-G-m5C-G-G-G-G-T-psi-C-G-A-C-U-C-C-C-C-G-C-A-A-C-G-G-A-G-C-C-AOH. The sequence differs markedly from that of S. cerevisiae tRNAGlu. S. pombe glutamate tRNA1 can be aminoacylated by the homologous glutaminyl-tRNA synthetase as well as by the corresponding enzyme from S. cerevisiae.     

Promotory effect of GA13 on flowering ofAmaranthus — a short day plant

Abstact The three plant types ofAmaranthus namely,A. caudatus f.albiflorus, A. caudatus f.caudatus andA. tricolor var.tristis are qualitative short day plants with critical photoperiods 16.0, 15.5 and 15.0 h, respectively. Gibberellins A₃, A₄₊₇ and A₁₃ affect extension growth, leaf differentiation and floral induction differently. Thus, in all the three plant types ofAmaranthus, whereas, GA₃ and G₄₊₇ enhanced extension growth, GA₁₃ was completely ineffective under both, 24- and 8-h photoperiods. None of the three gibberellins could affect the leaf differentiation. In all the three plant types, flowering was promoted by GA₁₃ and not by other gibberellins tried. GA₁₃ caused promotion was manifested in two manners, firstly by lowering the critical dark period requirement in each inductive cycle, and secondly by shortening the total period taken for the initiation of inflorescence primordia under inductive photoperiods. The floral induction by gibberellins inAmaranthus is contrary to the gibberellin-anthesin concept of Chailakhyan. It is suggested that gibberellins other than GA₃ may be playing an important role in floral morphogenesis of short day plants.     

Crystallization and Preliminary X-Ray Analysis of Rotavirus Protein VP6

As a first step to gain insight into the structure of the rotavirus virion at atomic resolution, we report here the expression, purification, and crystallization of recombinant rotavirus protein VP6. This protein has the property of polymerizing in the form of tubular structures in solution which have hindered crystallization thus far. Using a combination of electron microscopy and small-angle X-ray scattering, we found that addition of Ca²⁺ at concentrations higher than 100 mM results in depolymerization of the tubes, leading to an essentially monodisperse solution of trimeric VP6 even at high protein concentrations (higher than 10 mg/ml), thereby enabling us to search for crystallization conditions. We have thus obtained crystals of VP6 which diffract to better than 2.4 Å resolution and belong to the cubic space group P4₁32 with a cell dimension a of 160 Å. The crystals contain a trimer of VP6 lying along the diagonal of the cubic unit cell, resulting in one VP6 monomer per asymmetric unit and a solvent content of roughly 70%.