Transcription of naked double-stranded RNA molecules in a fraction containing large vesicles plus mitochondria from the basidiomycete Agrocybe aegerita

Abstract

Actinomycin D-resistant RNA synthesis was detected in the cellular (VM) fraction which contains large vesicles plus mitochondria from Agrocybe aegerita. It involved the RNAase-resistant complex of naked (unencapsidated) double-stranded RNAs (dsRNAs). The RNA polymerase assay showed [α-32P]UTP incorporation in dsRNAs of a size corresponding to the previously described naked M-dsRNAs and in single-stranded RNAs of related size, which are assumed to act as intermediaries in the replicative cycle of the dsRNA molecules. Moreover, the incorporation of ribonucleotides into large mitochondrial dsDNA fragments was detected in the dsRNA-containing strain. This result favours a mitochondrial location for the naked dsRNAs and their associated polymerizing enzyme(s). No replication of the encapsidated large L-dsRNA viral genome was detected in the VM fraction, supporting the hypothesis that the two types of dsRNAs observed in this A. aegerita strain are independent entities.