Tadahiko Kohno

Externally Suppressible Proline Quadruplet CCCUU

Three (+1) frameshift mutations located at different genetic sites respond with high specificity to the same external suppressor. In each case, the suppressor restores small amounts of protein that is normal in electrophoretic mobility and heat stability. One of these proteins has been shown to have the wildtype amino acid sequence. The messenger RNA quadruplet CCCUUappears to be common to all three frameshift sites and to be translated by the suppressor as proline. A likely suppressor agent is a proline transfer RNA with a quadruplet anticodon or its functional equivalent.

Proflavin mutagenesis of bacteria

Once a permeability barrier is overcome, proflavin is highly mutagenic for Salmonella typhimurium and Escherichia coli. Mutagenesis of the his operon (in Salmonella) and lac operon (in E. coli) depends on derepression of the respective operons. No proflavin mutagenesis was detected in rec− strains. Over 100 proflavin-induced his mutants have been classified: 50% are base substitution types, 30% are stable (10% demonstrably multisite), and only 20% are probably frameshift mutations. None of the proflavin-induced frameshift mutations is of the type previously shown to be suppressed by frameshift suppressor mutations.

A Salmonella frameshift suppressor that acts at runs of a residues in the messenger RNA

Abstract A Salmonella mutation is described that suppresses + 1 frameshift mutations in runs of A residues in the messenger RNA. The suppressor mutation is dominant and maps very close to the nag locus at minute 15 of the Salmonella chromosome. A lysine transfer RNA is known to map very close to this position. Since the frameshift suppressor appears allelic to a nonsense suppressor (UA(A/G)), it seems likely that the suppressor will prove to affect lysine tRNA (AA(A/G)).

Chemical and genetic studies on L-histidinol dehydrogenase of Salmonella typhimurium. Isolation and structure of the tryptic peptides.

Abstract l -Histidinol dehydrogenase from strain LT2 of Salmonella typhimurium has been studied. Sequence analysis has been carried out on the complete set of tryptic peptides from the reduced and carboxymethylated protein. Together with the nucleotide sequence of the corresponding gene (W. Barnes, unpublished results), the peptide sequences establish that the protein subunit is a single chain of 433 residues, with a molecular weight of 45,823.

A hotspot for spontaneous frameshift mutations in the histidinol dehydrogenase gene of Salmonella typhimurium.

Abstract A hotspot for spontaneous frameshift mutations in the histidinol dehydrogenase gene of Salmonella typhimurium contains two radically different types of frameshift. Reversion of each type occurs spontaneously but is not enhanced by the frameshift mutagens tested. One type, interpreted as extensive deletions, reverts at a very low frequency and produces only pseudo-wild type (+−) revertants in which histidinol dehydrogenase is either undetectable or cold-sensitive in vitro . The other type of frameshift, interpreted as duplications, reverts at a very high frequency and yields only apparently wild-type revertants with normal histidinol dehydrogenase. Neither type of frameshift appears to be externally suppressible. The hotspot contains a repeating DNA sequence of two to three G.C pairs and occasionally yields (+1) frameshift mutations with the acridine derivative, ICR-191, presumably by strand slippage. Slippage of greater extent may generate the complex spontaneous lesions.