Search PubMed⌕ Search

Biomedical subjects

D Schlessinger

Publications and source records attributed to D Schlessinger.

At least 271 records · Page 15Linked to original sources
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↗
PubMed1968

Coresistance to neomycin and kanamycin by mutations in an Escherichia coli locus that affects ribosomes.

Mutant strains resistant to neomycin or to kanamycin sulfate were isolated from Escherichia coli K-12. Nine mutants were analyzed; all were resistant to both antibiotics (about 150 and 100 mug/ml, respectively), and were designated nek. In the mutant strains, the ribosomes are changed from those of the parental strain; for when they were used in assays for polypeptide formation directed by polyadenylic acid or polycytidylic acid, coding fidelity in presence of the drugs was increased and inhibition of synthesis by the drugs was lessened. Mating experiments and transduction tests showed that all of the nine nek mutants are either closely linked or allelic, and the nek locus is closely linked to two genes-str (streptomycin) and spc (spectinomycin)-known to affect the 30S ribosome. The two nek mutants tested were recessive to the sensitive, wild-type allele. When the nek mutants were compared to the parental strain, pleiotropic effects of the nek mutations were observed. Resistance to low levels of streptomycin and spectinomycin was increased, whereas resistance to chloramphenicol was decreased. Also, the mutants were less able to adapt to high concentrations of lincomycin, and could no longer show phenotypic suppression of an arginine requirement by neomycin or kanamycin. Such pleiotropic effects are suggested to be the rule for mutations in genes that participate in the biosynthesis of a cellular organelle.

Alleles↗