Transcription of potato spindle tuber viroid by RNA polymerase II starts predominantly at two specific sites
AUTOR(ES)
Fels, Andreas
FONTE
Oxford University Press
RESUMO
Pospiviroidae, with their main representative potato spindle tuber viroid (PSTVd), are replicated via a rolling circle mechanism by the host-encoded DNA-dependent RNA polymerase II (pol II). In the first step, the (+)-strand circular viroid is transcribed into a (–)-strand oligomer intermediate. As yet it is not known whether transcription is initiated by promotors at specific start sites or is distributed non-specifically over the whole circle. An in vitro transcription extract was prepared from a non-infected potato cell culture which exhibited transcriptional activity using added circular PSTVd (+)-strand RNA as template. In accordance with pol II activity, transcription could be inhibited by α-amanitin. RT–PCR revealed the existence of at least two different start sites and primer extension identified these as nucleotides A111 and A325. The sequences of the first 7 nt transcribed are very similar, 105GGAGCGA111 and 319GGGGCGA325. GC-boxes are located at a distance of 15 and 16 nt upstream, respectively, in the native viroid structure, which may act to facilitate initiation. The GC-boxes may have a similar function to the GC-rich hairpin II in the (–)-strand intermediate, as described previously. The results are compared with the corresponding features of avocado sunblotch viroid, which belongs to a different family of viroids and exhibits different transcription initiation properties.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=92535Documentos Relacionados
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