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Biomedical subjects

D Apirion

Publications and source records attributed to D Apirion.

At least 109 records · Page 6Linked to original sources
PubMed1975

Escherichia coli ribosomal ribonucleic acids are not cut from an intact precursor molecule.

Ribonuclease III-deficient strains of Escherichia coli accumulate a "30 S" RNA species. Kinetic analysis of label incorporated into rRNA species shows, however, that 30 S RNA is not the major precursor to the 16 S and 23 S RNA species is in 7- to 10-fold excess over that into 30 S RNA. The 30 S RNA species turns over with a half-life of about 2.5 min, which could account for no more than one-tenth of the incorporation into 16 S plus 23 S RNA. Thus, under these conditions RNase III-strains of E. coli do not cut rRNAs from an intact tandem precursor molecule but rather from the elongating nascent transcript, possibly by an alternate pathway not involving RNase III.

Escherichia coli↗
PubMed1975

The fate of ribosomes in Escherichia coli cells starved for a carbon source.

The disappearance of ribosomes in Escherichia coli cells starved for a carbon source was studied. We used a series of mutants, some of them lacking in ribonuclease I(RNase I, EC 2.7.7.17), and other containing various combinations of modified polynucleotide phosphorylase (PNPase, EC 2.7.7.8) and modified ribonuclease II (RNase II, EC 3.1.4.1). RNA was prepared from the starved mutant cells and separated on polyacrylamide gels. The results obtained indicate that 23 S RNA degradation is similar in all strains that lack RNase I, and is slightly increased in the strain that contains this enzyme. The extent of 16 S RNA degradation is identical in all strains tested. RNA species in the size of 4 S and smaller accumulate in mutants containing modified forms of PNPase and RNase II. The appearance of an RNA species 10% smaller than 16 S RNA (d16 S RNA) was observed in all strains that contain unmodified RNase II. Analysis of ribosomes and polysomes and their RNA content indicated that polysomes are converted to monosomes and these, in turn, to ribosomal subunits. No RNA degradation products were found in polysomes, 70 S, OR 50 C particle; 30 S subunits contained 16 S RNA as well as the d16 S RNA species. Subunits are degraded to a similar extent in all strains lacking RNase I, and at a slightly faster rate in the strain that contains RNase I. The RNA to protein ratio in subunits prepared from starved cells is similar to that of unstarved cultures. Very little degradation of ribosomal proteins occurs in these mutants during carbon starvation. The proteins released from degraded ribosomes are found in the fast sedimenting (20,000 times g) pellet. Cell viability studies indicated a direct correlation between the capacity of the mutants to recovery from starvation and their capacity to degrade RNA. Thus a biological necessity for degradation of ribosomes during starvation is implied. Based on these data we propose that the endonucleolytic degradation of ribosomal RNA is the primary event in starvation degradation. It takes place in ribosomal subunits, which fall apart after the endonucleoltic attack. The RNA pieces produced by this cleavage are degraded to nucleotide by RNase II and PNPase. The ribosomal proteins attach to the cell membrane.

Bacterial Proteins↗
PubMed1975

Unaltered stability of newly synthesized RNA in strains of Escherichia coli missing a ribonuclease specific for double-stranded RNA.

Pairs of very closely related Escherichia coli strains were prepared, one having the wild-type allele for ribonuclease III, an enzyme which specifically degrades double-stranded RNA, and the other having a mutant RNase III allele. Growth and phage plating efficiency were compared in these strains. The RNase III+ strains grow better than the RNase III- strains and plate T7 and lambda phage better, but T4 plates with the same efficiency on both strains. On the other hand, the half lives of newly synthesized RNA as well as of functional beta-galactosidase mRNA are similar in both kind of strains. These two parameters, however, are significantly longer in both strains as compared to the original strain from which they were derived. Also, no difference in the differential induction of beta-galactosidase was observed between such strains. Thus, we have to conclude that either ribonuclease III does not play a significant role in the functioning and stability of newly synthesized mRNA, or that enough enzymatic activity was left, residual RNase III or some other enzyme to deal with double-stranded regions in the message.

Enzyme Induction↗
PubMed1975

Mapping and characterization of a mutation in Escherichia coli that reduces the level of ribonuclease III specific for double-stranded ribonucleic acid.

Localization of a mutation affecting ribonuclease III activity (an enzyme specific for double-stranded ribonucleic acid) in Escherichia coli was attempted. By a series of matings and transduction experiments, the mutation rnc-105 was mapped near the nadB gene. In strains carrying this mutation, another mutation (ranA2074) was also found. Based on available data, their order on the E. coli chromosome appears to be tyrA, ranA, nadB, rnc, purI. Strains carrying either the ranA2074 or the rnc-105 mutation fail to grow at 45 C in enriched medium, whereas strains carrying only the rnc-105 mutation are defective in ribonuclease III activity. Strains carrying either of these mutations grow more slowly than corresponding wild-type strains in all media tested at all temperatures; the rnc-105 mutation reduces the growth rate more than the ranA2074 mutation. T4 and T7 bacteriophages form plaques with a lower efficiency on strains carrying the rnc-105 mutation than on other strains. Thus we suggest that ribonuclease III is beneficial for normal growth of E. Coli and that at higher temperatures it becomes indispensable.

Chromosome Mapping↗
PubMed1974

A technique for the isolation of mutants of Escherichia coli affected in degradation of cellular RNA.

Using a semiautomatic technique for handling large numbers of Escherichiacoli colonies, mutants that fail to digest their cellular RNA were isolated. This was achieved by using multiwell plates where each colony is cloned in an individual well. Cells labeled with a radioactive RNA precursor were starved for a carbon source at a high temperature. In order to assess whether or not degradation of cellular RNA took place, aliquots of each culture were subjected to autoradiography. A number of mutants defective in decay of RNA were isolated. One of them was characterized, and was found to be deficient specifically in the enzyme polynucleotide phosphorylase. Experiments carried out with this strain indicate that this enzyme participates in the degradation of "stable" RNA during carbon starvation.

Bacterial Proteins↗