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Biomedical subjects

A Skalka

Publications and source records attributed to A Skalka.

28 records · Page 2Linked to original sources
PubMed1969

The molecular origin of lambda prophage mRNA.

Lambda-specific RNA extracted from lysogenic bacteria hybridizes specifically with fragments of lambda DNA containing 43 per cent GC (guanine plus cytosine). Therefore genes known to function in the prophage state (c(I) and rex) lie 0.38 +/- 0.08 fractional molecular length from the right end of the lambda DNA molecule, according to the compositional map of Skalka, Burgi, and Hershey.

Centrifugation, Density Gradient↗
PubMed1969

Nucleotide distribution and functional orientation in the deoxyribonucleic acid of phage phi 80.

The distribution of nucleotides in the deoxyribonucleic acid (DNA) of phi80 was determined by density analysis of molecular fragments of known length and origin. One half of the molecule includes a long, fairly homogeneous segment that contains 55% guanine plus cytosine (GC). DNA in the other half contains about 50% GC, except for a short stretch near the molecular end where the GC content is higher. Transcription of phi80 DNA was studied by ribonucleic acid-DNA hybridization tests with isolated molecular halves. At times early in the growth cycle, messenger is synthesized at a constant, relatively low rate and originates almost exclusively from DNA in the lower-GC half. At later times, messenger represents both halves and is synthesized at a greatly increased rate. The DNA of phi80 is closely analogous, physically and functionally, to lambda DNA. The similarity is most striking in the high-GC half, which is defined here as "left" since its molecular end contains a cohesive site homologous to that at lambda's left end. The left halves of the DNA of the two phages contain primarily late-functioning genes, and possess similar nucleotide distributions and some similar base sequences. The right halves of the two DNA molecules are less similar. Both contain the early genes, but they differ considerably in GC content (45% in lambda, 51% in phi80) and do not strongly cross-react in hybridization tests. The DNA of phi80 lacks the central 37%-GC segment found in lambda.

Coliphages↗
PubMed1966

Some properties of DNA from phage-infected bacteria.

Replicating T5 or lambda phage DNA has been labeled by adding tritiated thymidine for short periods to cultures of phage-infected Escherichia coli before isolation of intracellular DNA. Two procedures are described for separating T5 replicating DNA from DNA of intracellular phage particles. Both T5 and lambda replicating DNA had the same bouyant density in cesium chloride as DNA from phage particles but sedimented faster when centrifuged in sucrose density gradients. The fast sedimentation did not appear to be caused by DNA protein or DNA-RNA complexes or by aggregation of DNA, but is probably due to DNA molecules of unusual structure. Experiments involving hydrodynamic shear and sucrose density gradient centrifugation at alkaline pH have suggested that with lambda the replicating form of DNA is a linear molecule considerably longer than the DNA molecules of lambda-phage particles. The constituent polynucleotide chains of lambda but not T5 replicating DNA also appear to be longer than those of phage DNA.

Centrifugation, Density Gradient↗