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Biomedical subjects

J R Roth

Publications and source records attributed to J R Roth.

At least 109 records · Page 6Linked to original sources
PubMed1982

Transposon Tn10 provides a promoter for transcription of adjacent sequences.

Promoters located within the Tn10 insertion element cause transcription of "host" sequences adjacent to both ends of the inserted Tn10 element. These promoters are usually not observed in genetic experiments because their transcripts are efficiently terminated at nearby rho-dependent termination sites. The observations presented here provide an explanation for several confusing aspects of transposon behavior and suggest the possibility that many transposons possess promoters that have escaped detection for similar reasons.

DNA Transposable Elements↗
PubMed1981

Four-base codons ACCA, ACCU and ACCC are recognized by frameshift suppressor sufJ.

The frameshift suppressor sufJ acts to correct a set of +1 frameshift mutations having very different sequences at their mutant sites. This suppressor acts by reading a 4 base codon located near, but not at, the site of each suppressible mutation. Suppression thus necessitates out-of-phase translation of the short stretch of mRNA between the site of action of the suppressor tRNA and the site of the frameshift mutation. We have identified the site read by sufJ by mutationally creating a series of such sites in the neighborhood of a previously nonsuppressible frameshift mutation. Each of the newly generated sites was formed by base substitution. Four independently generated sites were analyzed by DNA sequencing. At each site the quadruplet codon ACCX was generated (where X is A, U or C). Thus sufJ is able to read a 4 base codon in which any of three bases is acceptable in the fourth position. This is the first frameshift suppressor that does not read a run of three repeated bases in the first three positions of its codon.

Base Sequence↗
PubMed1981

Trypsin enhancement of rotavirus infectivity: mechanism of enhancement.

The infectivity of most rotaviruses is enhanced by treatment with trypsin. We studied the mechanism of enhancement of examining the effect of trypsin on rotavirus infectivity, aggregation, early interactions with host cells, and structure. The results indicated that trypsin does not increase levels of infectious virus by dispersion of aggregates or affect the efficiency or rate of attachment of virus to cells. A fraction of virus that was not infections without trypsin treatment was found to attach to cells, but did not initiate antigen synthesis. When cells were infected with labeled, purified virus, increased levels of uncoated particles were found in cells infected with trypsin-treated virus. Infection of cells with trypsin-treated virus also led to greater levels of RNA synthesis early in the infection. The results suggest that trypsin converts a noninfectious fraction of virus into infectious virus by allowing this fraction to uncoat in the infected cell. Trypsin was found to cleave an 88,000-dalton structural polypeptide of bovine rotavirus generating 67,000- and 20,000-dalton cleavage products.

Animals↗
PubMed1980

The influence of codon context on genetic code translation.

A class of mutations that increase the deficiency of a suppressor tRNA in translating a particular amber codon has been characterized. The increased efficiency is due to a mutation resulting in a change in the mRNA that affects the nucleotide adjacent to the 3' side of the UAG triplet. Thus the interaction of tRNA with mRNA is influenced by mRNA sequences outside the triplet codon.

Base Sequence↗
PubMed1980

Model for regulation of the histidine operon of Salmonella.

A model is proposed that accounts for regulation of the histidine operon by a mechanism involving alternative configuration of mRNA secondary structure (the alternative stem model). New evidence for the model includes sequence data on three regulatory mutations. The first (hisO1242) is a mutation that deletes sequences needed to form the attenuator mRNA stem and causes constitutive operon expression. The second mutation (hisO9654) is a His- ochre (UAA) mutation in the leader peptide gene; the existence of this mutation constitutes evidence that the leader peptide gene is translated. The third mutation (hisO9663) is remarkable. It neither generates a nonsense codon nor affects a translated sequence; yet, it is suppressible by amber suppressors. We believe this mutation causes a His- phenotype by interfering with mRNA secondary structure. The suppressibility of the mutation is probably due to disruption of the attenuator stem by ribosomes that read through the terminator codon of the leader peptide gene. This explanation is supported by the observation of derepression of a wild-type control region in the presence of an amber suppressor. Evidence is presented that hisT mutants (which lack pseudouridine in the anticodon arm of histidine tRNA) may cause derepression of the his operon by slowing protein synthesis in the leader peptide gene.

Bacterial Proteins↗
PubMed1980

Regulation of Tn5 transposition in Salmonella typhimurium.

The drug-resistance element Tn5 transposes with high frequency immediately after entry into a cell. Establishment of Tn5 within a cell results in a decrease in this transposition frequency. This phenomenon resembles "zygotic induction" of repressible operons and prophages. Evidence is presented that Tn5 transposition is under negative control by a factor encoded within the element itself. Established Tn5 elements (that contain point mutations inactivating the resistance gene) are able to inhibit transposition of an incoming Tn5 element by a factor of 12- to 70-fold. Several deletion derivatives of Tn5 lack the ability to inhibit transposition.

DNA Transposable Elements↗
PubMed1980

UGA suppressor that maps within a cluster of ribosomal protein genes.

A suppressor of UGA mutations (supU) maps near or within a cluster of ribosomal protein genes at 72 min on the Salmonella typhimurium genetic map. The suppressor is relatively inefficient, and its activity is abolished by rpsL (formerly strA) mutations. The suppressor is dominant to a wild-type supU allele. The map position of this suppressor suggests that it may owe its activity to an alteration of ribosome structure.

Bacterial Proteins↗
PubMed1979

Histidine mutants requiring adenine: selection of mutants with reduced hisG expression in Salmonella typhimurium.

A method is described for the selection of Salmonella typhimurium mutants with reduced levels of hisG enzyme activity. This method is based on the fact that the hisG enzyme catalyzes the consumption of ATP in the first step of histidine biosynthesis. Normally, this reaction is closely regulated, both by feedback inhibition and by repression of the operon. However, conditions can be set up that result in the uncontrolled use of adenine in histidine biosynthesis. Cells grown under these conditions become phenotypic adenine auxotrophs. Some revertant clones that no longer require adenine contain mutations in hisG, hisE, or the his-control region. The hisG mutations are of all types (nonsense, frameshift, missense, deletion and leady types), and they map throughout the hisG gene.

ATP Phosphoribosyltransferase↗
PubMed1979

A refined map of the hisG gene of Salmonella typhimurium.

The hisG gene is the most operator-proximal structural gene of the histidine operon; it encodes the feedback-inhibitable first enzyme of the biosynthetic pathway. Previously, hisG mutants were mapped into seven intervals defined by the availble deletion mutations having endpoints in the hisG gene. The map has been refined using over 60 new deletion mutants. The new map divides the gene into 40 deletion intervals, which average approximately 30 base pairs in length. The map has been used to analyze the distribution of insertion sites for the transposable element Tn10 and has permitted conclusions on the diistribution of duplication endpoints. The map promises to be useful in analysis of his regulation and, more particularly, in the determination of the possible role of the hisG enzyme in this mechanism.

ATP Phosphoribosyltransferase↗