Viroids are small (246-401 nucleotides), non-coding, circular RNAs able to replicate autonomously in certain plants. Viroids are classified into the families Pospiviroidae and Avsunviroidae, whose members replicate in the nucleus and chloroplast, respectively. Replication occurs by an RNA-based rolling-circle mechanism in three steps: (1). synthesis of longer-than-unit strands catalyzed by host...

The hepatitis delta virus genome is a small circular RNA, similar to viroids. Although HDV contains a gene, the protein produced (HDAg) is encoded by less than half the genome and possesses no RNA polymerase activity. Because of this limited coding capacity, HDV relies heavily on host functions and on structural features of the viral RNA-very much like viroids. The virus' use of host RNA editin...

A factorial experiment begun in 1980 included ‘Hamlin’ and ‘Valencia’ sweet-orange scions [Citrus sinensis (L.) Osb.], and Milam lemon (C. jambhiri Lush) and Rusk citrange [C. sinensis x Poncirus trifoliata (L.) Raf.] rootstocks, tree topping heights of 3.7 and 5.5 m, between-row spacings of 4.5 and 6.0 m, and in-row spacings of 2.5 and 4.5 m. The spacing combinations provided tree densities of...

1 Department of Biological Sciences, Mississippi State University, Starkville, Mississippi, United States of America, 2 Department of Mathematics and Statistics, Bowling Green State University, Bowling Green, Ohio, United States of America, 3 Department of Chemistry and Center for Biomolecular Sciences, Bowling Green State University, Bowling Green, Ohio, United States of America, 4 Department ...

On San Miguel, one of the smallest of the 7 000 islands of the Philippines, a few coconut palms were slowly dying in 1928. Ten years later, 50 000 palms on this island were dead or dying. The disease seemed to be limited to a certain area and affected only coconut palms. No bacteria or fungi were found to be associated with the dying palms. The disease, believed to be caused by a virus, began t...

The sequence of the 356 nucleotide residues of chrysanthemum stunt viroid (CSV) has been determined. Overlapping linear viroid fragments were obtained by partial ribonuclease digestion, radiolabelled in vitro at their 5'-ends, and sequenced using partial enzymic cleavage methods. Of the CSV sequence, 69% is contained in the published sequence of potato spindle tuber viroid (PSTV). Differences i...

We suggest that viroids are trapped into adaptive peaks as the result of adaptive constraints. The first one is imposed by the necessity to fold into packed structures to escape from RNA silencing. This creates antagonistic epistases, which make future adaptive trajectories contingent upon the first mutation and slow down the rate of adaptation. This second constraint can only be surpassed by i...