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Localization of Viral RNA Polymerase Activity and its Products in Extracts of Barley Leaves Infected with Bromegrass Mosaic Virus. J. Semal, Associate Professor, Faculté des Sciences agronomiques, 5800 Gembloux, Belgium; J. Kummert(2), and D. Dekegel(3). (2)Research Assistant, Faculté des Sciences agronomiques, 5800 Gembloux, Belgium; (3)Reader, Institut Pasteur and Vrije Universiteit, 1050 Brussels, Belgium. Phytopathology 64:446-451. Accepted for publication 19 September 1973. DOI: 10.1094/Phyto-64-446.

The pulse-labeled, double-stranded RNA product of the virus-specific RNA polymerase activity in extracts of barley leaves infected with bromegrass mosaic virus was found to be bound to particulate material which sedimented at 10,000 g. However, after a chase, part of the pulse-chased product was released in the 10,000 g supernatant as single-stranded RNA. Further fractionation of the standard RNA polymerase preparation by centrifugation in a discontinuous sucrose gradient showed that both the virus-specific, actinomycin-resistant, RNA polymerase activity and the pulse-labeled RNA products accumulated at the interphase between the 25% and the 45% sucrose. Whole organelles were not present in the active fraction, which contained essentially chloroplast debris together with various membranous and vesicular structures. Similar structures were found in comparable preparations made from healthy leaves, the latter being devoid of actinomycin-resistant RNA polymerase activity. Treatment with sodium deoxycholate dissociated most of the pulse-labeled RNA product from the 10,000 g pellet to which it was bound, while most of the green pigment remained sedimentable at 10,000 g after such treatment. It is suggested that the subcellular structures involved in the synthesis of virus-specific RNA are distinct from the bulk of pigment-bearing chloroplast debris.