In vitro transcription of a transfer RNA gene

The Escherichia coli tRNA(Tyr) gene carried by the varphi80psu(3) + transducing phage was transcribed in vitro by DNA-dependent RNA polymerase. The enzymatically synthesized tRNA(Tyr)-like polynucleotide chains were detected by competition with purified E. coli(32)P-tRNA(Tyr) for specific hybridization sites on varphi80psu(3) + DNA. Analysis by sucrose gradient centrifugation showed the tRNA(Tyr)-like chains to possess a heterogeneous distribution with respect to sedimentation coefficients, with a broad peak around 8 S. The presence of the termination factor rho during the transcription did not significantly reduce the average size of the in vitro synthesized tRNA(Tyr)-like chains.

Perchloric acid extraction of deoxyribonucleic acid from thin sections of epon-araldite-embedded material

A method is presented for the extraction of deoxyribonucleic acid from thin sections of tissue fixed in glutaraldehyde and osmium tetroxide and embedded in water-insoluble epoxy resin. Incubation of thin sections in 20% perchloric acid at 60°C for 8 hr produced electron-transparent bands in the polytene chromosomes from Drosophila salivary glands. Chromosome bands were also rendered electron-transparent when hydroxypropylmethacrylate-embedded thin sections were digested with deoxyribonuclease or extracted with perchloric acid. Nucleolar ribonucleic acid was unaffected by the perchloric acid extraction.

Purification of Neurospora crassa endonuclease-resistant DNA-RNA hybrid

Denatured calf thymus DNA has been transcribed in vitro with RNA polymerase of Micrococcus lysodeikticus. The DNA–RNA hybrid which formed in this system was found to be highly resistant to a purified Neurospora crassa endonuclease, while the unhybridized DNA and RNA were rapidly degraded. DNA–RNA hybrid with a purity of 62–75% was isolated in one step from the digest in 69–86% yield by chromatography on methylated albumin – kieselguhr. Further purification was obtained by density gradient centrifugation in Cs2SO4 solution. The purified hybrid had a buoyant density of 1.49 g cm−3 in Cs2SO4, intermediate between that of mouse tRNA marker (1.63 g cm−3) and calf thymus DNA (1.43 g cm−3). During sucrose density gradient centrifugation, the hybrid sedimented slightly faster than mouse tRNA marker. Evidence for the double-stranded nature of the hybrid was found by thermal denaturation of the complex. The RNA of the hybrid became increasingly sensitive to ribonuclease as the hybrid was heated at successively higher temperatures.

Changes in the macromolecular structure of DNA-RNA-protein complexes induced by gel-filtration on sephadex G-25

Hydrodynamic shearing forces appearing during nucleoprotein gel-filtration on Sephadex G-25 cause a disruption of the macromolecular structure in nucleoproleins.

The effect of these shearing forces can be observed both in electron micrographs and by electro­phoretic analysis.

The decrease of the molecular weight and also the changes in the electronegative charge,mole­cular weight ratio cause an increase of the electrophoretic mobility of the gel-filtered highly poly­merized DNA and of the RNA complexed to it compared with the not gel-filtered nucleoprotein.