We have developed a simple, rapid, and reliable protocol for the small-scale purification of DNA and RNA from, e.g., human serum and urine. The method is based on the lysing and nuclease-inactivating properties of the chaotropic agent guanidinium thiocyanate together with the nucleic acid-binding properties of silica particles or diatoms in the presence of this agent. By using size-fractionated silica particles, nucleic acids (covalently closed circular, relaxed circular, and linear double-stranded DNA; single-stranded DNA; and rRNA) could be purified from 12 different specimens in less than 1 h and were recovered in the initial reaction vessel. Purified DNA (although significantly sheared) was a good substrate for restriction endonucleases and DNA ligase and was recovered with high yields (usually over 50%) from the picogram to the microgram level. Copurified rRNA was recovered almost undegraded. Substituting size-fractionated silica particles for diatoms (the fossilized cell walls of unicellular algae) allowed for the purification of microgram amounts of genomic DNA, plasmid DNA, and rRNA from cell-rich sources, as exemplified for pathogenic gram-negative bacteria. In this paper, we show representative experiments illustrating some characteristics of the procedure which may have wide application in clinical microbiology.

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The rate of initiation of protein synthesis appears to be controlled at the level of recycling of eIF-2. In this process a new factor, designated eRF, plays an important role. The factor has been purified from the postribosomal supernatant and has been called formerly anti-HRI and anti-inhibitor [Amesz, H., Goumans, H., Haubrich-Morree, Th., Voorma, H. O., and Benne, R. (1979) Eur. J. Biochem. 98, Its effect on the initiation of protein synthesis has been studied in several assays: a small but distinct effect is found in the assay for the formation of a ternary complex between eIF-2, GTP and Met-tRNA; a 4-Sfold stimulation is obtained in assays for 40s preinitiation complex formation and in the methionyl-puromycin reaction. In the latter assay a catalytic use of eIF-2 occurs provided that eRF is present.eRF forms a complex with eIF-2 which results in a decrease of the affinity of eIF-2 for GDP, giving it the properties of a GDP/GTP exchange factor. The model stresses the catalytic use of eIF-2 in initiation provided that conditions are met for GDP/GTP exchange by a transient complex formation between eIF-2 and eRF. On the other hand, it is shown that phosphorylation of eIF-2 by the hemin-regulated inhibitor (HRI) abolishes the recycling of eIF-2, by the formation of another stable complex comprising eIF-2aP, GDP and eRF.In recent years, an impressive amount of data has accumulated on the components involved in the initiation of protein synthesis in mammalian cells (for reviews, see [1 -31). The sequence of events comprising the construction of an initiation complex requires the participation of at least nine protein factors called eIF-1, -2, -3, -4A, -4B, -4C, -4D, -4E, -4F and -5. Many papers have dealt with the detailed description of the intricate manner in which initiation factors contribute in the assembly of an 80s initiation complex [l -51. In brief, the pathway leads through (a) formation of a ternary complex between eIF-2, Met-tRNA and GTP, (b) subsequent combination of this complex with a preformed complex of the 40s ribosomal subunit, eIF-3 and eIF-4C 161, (c) binding of the messenger with the aid of eIF-1 [5, 71, 91, and (d) eIF-5-mediated junction of the 40s complex and the 60s ribosomal subunit [4, 51.Very little, however, was known about the way this process is regulated. Most of the information acquired is derived from reticulocyte lysates in which the absence of hemin leads to the cessation of protein synthesis [lo, 111. This cessation is caused by the action of an inhibitor called hemin-regulated inhibitor, HRI [12, 131, which phosphorylates the small (Mr 36000) asubunit of eIF-2 [14-171. A causal relation between the halt of globin synthesis and the phosphorylation of eIF-2 appears to exist, since the addition of purified eIF-2 to a hemindeprived lysate results in relief of the inhibition [18-201, but until recently no difference in biological activity between purified phosphorylated eIF-2 and control eIF-2 could be detected in model assay systems and the crude Iysate system [23 -231.We have...

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