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DNA showed a 20 per cent decrease in the incorporation of labelled UMP while under the conditions for the RNAprimed reaction there was a slight increase in incorporation.No apparent differences were observed in the activities of DNA nucleotidyltransferase or DNA-primed RNA nucleotidyltransferase in preparations from infected and uninfected cells and cell fractions (Fig. 1a, b). However, significant increases in RNA-primed RNA nucleotidyltransferase activity were observed in each of the five experiments of this type performed beginning at intervals of 1-3 h after infection (Fig. 1c). The increases were more pronounced in enzyme preparations from nuclear than cytoplasmic fractions.Reich, Franklin, Shatkin and Tatum• have demonstrated that more than 90 per cent of DNA-primed RNA synthesis can be inhibited by actinomycin D in L cells without significant interference with the production of an infectious RNA virus. More recently, Baltimore and Franklin 7 have found that after infection of L cells with mengovirus there is increased incorporation of ribonucleotide residues into polyribonucleotides by a particulate fraction from the cell cytoplasm. These pieces of evidence, together with the finding that RNA-primed RNA nucleotidyltransferase activity is increasod in Krebs II ascites tumour cells on infection with encophalomyocarditis virus, suggest that the rtplication of RNA viruses, at least in some mammalian systems, is dependent on RNA-primed rather than on DNA-primed synthesis of RNA.

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Regions in the cortex of some keratin fibres are shown to contain a relatively high proportion of non-keratinous material. The microfibrillar orientation in these regions is shown to be biaxial in nature and, in addition, areas of amorphous material are reported. Calcium salts, in particular hydroxyapatite, have been located and identified using electron diffraction, which has also proved valuable in correlating the incidence of some non-keratinised cells in the inner part of the cortex with the histochemical properties of this region. A comparison is made between the environment of the sites of calcification in keratin with those in collagen and elastin.Key words: Calcification --Hydroxyapatite --Keratin --Hair --Electron diffraction.Certaines r6gions du cortex des fibres de k6ratine contiennent une proportion relativement 61ev6e de mat6riel non k6ratinis6. L'orientation microfibrillaire dans ces r6gions est biaxiale et on y trouve, en outre, des zones de mat6riel amorphe. Les sels calciques, et en particnlier l'hydroxyleapatite, sont 6tudi6s par diffraction 61ectronique qui permet de les localiser et de les identifier. En ontre, cette technique permet de d6terminer la fr6quence de cellules nonk6ratinis6es clans la partie interne du cortex et de les comparer avec les propri6t6s histochimiques de cette r6gion. Une comparison est effectu6e entre la calcification de ]a k6ratine et celle int6ressant le collag~ne et l%lastine.Es wird gezeigt, dab Bereiche im Cortex yon gewissen Keratinfasern einen relativ hohen Anteil an nichtkeratinSsem Material enthalten. Ferner konnte nachgewiesen werden, dab die Orientierung der Mikrofibrillen in diesen Bereichen biaxia]er Art ist, und dal3 Bezirke yon amorphem Material vorhanden sind. Die Caleiumsalze und insbesondere das Hydroxyapatit konnten mit Hilfe der Elektronendiffraktion lokalisiert und identifiziert werden. Diese Methode hat sich auch als wertvoll erwiesen, um die Wechselbeziehung zwischen dem Vorkommen von einigen nichtkeratinisierten Zellen im Cortexinnern und den histochemischen Eigenschaften dieser Regionen zu zeigen. Ein Vergleich wird gemacht zwischen der Umgebung der Verkalkungsstellen im Keratin mit derjenigen im Kollagen und im Elastin.