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Biomedical subjects

D Apirion

Publications and source records attributed to D Apirion.

At least 145 records · Page 8Linked to original sources
PubMed1971

Genetic analysis of an Escherichia coli syndrome.

A mutant strain of Escherichia coli that fails to recover from prolonged (72 hr) starvation also fails to grow at 43 C. Extracts of this mutant strain show an increased ribonuclease II activity as compared to extracts of the parental strain, and stable ribonucleic acid is degraded to a larger extent in this strain during starvation. Ts(+) transductants and revertants were tested for all the above-mentioned phenotypes. All the Ts(+) transductants and revertants tested behaved like the Ts(+) parental strain, which suggests that all the observed phenotypes are caused by a single sts (starvation-temperature sensitivity) mutation. The reversion rate from sts(-) to sts(+) is rather low but is within the range of reversion rates for other single-site mutations. Three-point transduction crosses located this sts mutation between the ilv and rbs genes. The properties of sts(+)/sts(-) merozygotes suggested that the Ts(-) phenotype of this mutation is recessive.

Carbon Isotopes↗
PubMed1970

Ribonuclease V of Escherichia coli: susceptibility of heated ribosomal RNA and stability of R17 phage RNA.

Native ribosomal RNA anid inttact pliage R17 RNA are insensitive to attack by ribonuclease V, an exonucleolytic activity associated with ribosome movement on the substrate RNA. However, ribosomal RNA becomes a substrate when it is heated under conditions that make it a template for protein synthesis, and R17 RNA is attacked if it is either heated or fragmnented. Accessibility of the 5' terminus of an RNA molecule is probably inzcreased by heating or fragmnentation and may determine its susceptibility to ribonuclease V.

Coliphages↗
PubMed1969

Mutants in Escherichia coli ribosomes: a new selection.

Only a few ribosome genes have been identified. Increasing the available kinds of ribosome mutants would thus facilitate the analysis of specification and function of the organelle. In an attempt to reveal a number of ribosome genes, we sought mutants that could not form functional ribosomes at a nonpermissive temperature (43 degrees ). Cells were depleted of ribosomes by nutrient starvation at 43 degrees , and 98 strains that could not recover from the starvation were then isolated. Of these 98, many satisfied auxiliary criteria for ribosome mutants; 23 showed increased sensitivity to antibiotics that affect ribosome function; and 8 of 20 representative strains had crude extracts more temperature sensitive than that of the parental strain when assayed for polyphenylalanine formation in the presence of excess soluble enzymes (S100) of the parental strain. In further tests with two of these strains, the temperature sensitivity of the washed ribosomes, compared to that of the parental strain, was confirmed. The variety of phenotypes among the mutants suggests that this selection is capable of revealing mutants in many ribosome genes.

Anti-Bacterial Agents↗
PubMed1969

Functional interdependence of ribosomal components of Escherichia coli.

Ribosomes are made up of parts that interact so strongly that a mutation in one of them can mask the effect of mutation in another. For example, when a mutation to neomycin resistance, which is a ribosome mutation, is introduced into cells carrying a ribosome mutation to spectinomycin resistance, some of the doubly mutant strains were phenotypically sensitive to spectinomycin, even though the mutation to spectinomycin resistance is still intact and recoverable in appropriate crosses. The neomycin mutant alleles that cause masking were shown by genetic tests to be in an identified locus that affects ribosomes. Protein synthesis in cell-free extracts of a double mutant strain was as sensitive to the action of spectinomycin as was the extract of the doubly sensitive parental strain. Thus, the masking effect of neomycin mutations on the spectinomycin mutation is exerted at the level of the ribosomes.We conclude that the genetic analysis of an organelle like the ribosome is likely to be severely complicated by pleiotropic effects and by interactions among its component parts and that the ribosomal binding sites for spectinomycin and neomycin are partially interdependent. These results suggest that the function of the ribosome requires a very precise conformation of all its elements, some of which are interdependent. Modification in one element can thus alter the function of another or even render the entire structure nonfunctional.

Binding Sites↗
PubMed1969

Ribonuclease V of escherichia coli. I. Dependence on ribosomes and translocation.

A new RNase activity, tentatively named RNase V, was found in cell-free extracts of E. coli. This activity requires ribosomes, G and T factors, tRNA, K(+) or NH(4) (+), Mg(2+), GTP, and a sulfhydryl compound to degrade poly U, poly A, T4 phage mRNA, or E. coli mRNA. RNase V is specific for mRNA; it does not attack ribosomal RNA. It is inhibited by antibiotics that decrease breakdown of mRNA in vivo, such as chloramphenicol and streptomycin, and by such agents as 5'-beta, gamma-methylene-guanosine triphosphate, and fusidic acid, which inhibit ribosome-dependent GTPase and translocation of ribosomes along mRNA. The evidence suggests that RNase V is either an integral part of the ribosome or is tightly associated with it, and that it selectively degrades mRNA in intact cells.

Anti-Bacterial Agents↗
PubMed1969

Streptomycin action: greater inhibition of Escherichia coli ribosome function with exogenous than with endogenous messenger ribonucleic acid.

Inhibition of protein synthesis by streptomycin was tested in extracts from a strain of Escherichia coli sensitive to streptomycin. Three kinds of messenger ribonucleic acid (RNA) were employed: endogenous cellular RNA, extracted cellular RNA, and phage R17 RNA. Protein synthesis directed by extracted cellular RNA was inhibited three- to fourfold more than protein synthesis directed by endogenous RNA. With R17 RNA as messenger, nearly total inhibition of protein synthesis at initiation was again observed. The greater inhibition of function of extracted RNA, which must initiate new polypeptide chains in vitro, is in accord with the observation that in whole cells streptomycin blocks ribosomes at an early stage in protein synthesis. When streptomycin was added at successively later times during protein synthesis, the subsequent inhibition was progressively less. This was observed with either extracted cellular RNA or phage R17 RNA. A model is presented that can explain the less drastic inhibition by streptomycin of messenger RNA that is already functioning on ribosomes.

Alanine↗