6 research outputs found
Rolling-circle replication of viroids, viroid-like satellite RNAs and hepatitis delta virus: variations on a theme
Viroids and viroid-like satellite RNAs from plants, and the human hepatitis delta virus
(HDV) RNA share some properties that include small size, circularity and replication
through a rolling-circle mechanism. Replication occurs in different cell compartments
(nucleus, chloroplast and membrane-associated cytoplasmatic vesicles) and has three steps:
RNA polymerization, cleavage and ligation. The first step generates oligomeric RNAs that
result from the reiterative transcription of the circular templates of one or both polarities,
and is catalyzed by either the RNA-dependent RNA polymerase of the helper virus on which
viroid-like satellite RNAs are functionally dependent, or by host DNA-dependent RNA
polymerases that, remarkably, viroids and HDV redirect to transcribe RNA templates.
Cleavage is mediated by host enzymes in certain viroids and viroid-like satellite RNAs,
while in others and in HDV is mediated by cis-acting ribozymes of three classes. Ligation
appears to be catalyzed mainly by host enzymes. Replication most likely also involves many
other non-catalytic proteins of host origin and, in HDV, the single virus-encoded protein.This work was supported by the Ministerio de Ciencia e Innovación of Spain (grant
BFU2008-03154/BMC) and by the Generalidad Valenciana (ACOMP/2010/278) to R.F, by
the National Science Foundation of the USA (grant IRFP-0602042) to D.G, and by the
Agencia Española de Cooperación Internacional (A/022313/08) to A.E. Due to space
limitations we have been unable to refer to the original work of many authors and, instead,
we have recurred to reviews. We apologize for any inconvenience this may have caused.Peer reviewe
Viroid Replication: Rolling-Circles, Enzymes and Ribozymes
Viroids, due to their small size and lack of protein-coding capacity, must rely essentially on their hosts for replication. Intriguingly, viroids have evolved the ability to replicate in two cellular organella, the nucleus (family Pospiviroidae) and the chloroplast (family Avsunviroidae). Viroid replication proceeds through an RNA-based rolling-circle mechanism with three steps that, with some variations, operate in both polarity strands: i) synthesis of longer-than-unit strands catalyzed by either the nuclear RNA polymerase II or a nuclear-encoded chloroplastic RNA polymerase, in both instances redirected to transcribe RNA templates, ii) cleavage to unit-length, which in the family Avsunviroidae is mediated by hammerhead ribozymes embedded in both polarity strands, while in the family Pospiviroidae the oligomeric RNAs provide the proper conformation but not the catalytic activity, and iii) circularization. The host RNA polymerases, most likely assisted by additional host proteins, start transcription from specific sites, thus implying the existence of viroid promoters. Cleavage and ligation in the family Pospiviroidae is probably catalyzed by an RNase III-like enzyme and an RNA ligase able to circularize the resulting 5′ and 3′ termini. Whether a chloroplastic RNA ligase mediates circularization in the family Avsunviroidae, or this reaction is autocatalytic, remains an open issue
Rolling-circle replication of viroids, viroid-like satellite RNAs and hepatitis delta virus: variations on a theme
Viroids and viroid-like satellite RNAs from plants, and the human hepatitis delta virus
(HDV) RNA share some properties that include small size, circularity and replication
through a rolling-circle mechanism. Replication occurs in different cell compartments
(nucleus, chloroplast and membrane-associated cytoplasmatic vesicles) and has three steps:
RNA polymerization, cleavage and ligation. The first step generates oligomeric RNAs that
result from the reiterative transcription of the circular templates of one or both polarities,
and is catalyzed by either the RNA-dependent RNA polymerase of the helper virus on which
viroid-like satellite RNAs are functionally dependent, or by host DNA-dependent RNA
polymerases that, remarkably, viroids and HDV redirect to transcribe RNA templates.
Cleavage is mediated by host enzymes in certain viroids and viroid-like satellite RNAs,
while in others and in HDV is mediated by cis-acting ribozymes of three classes. Ligation
appears to be catalyzed mainly by host enzymes. Replication most likely also involves many
other non-catalytic proteins of host origin and, in HDV, the single virus-encoded protein.This work was supported by the Ministerio de Ciencia e Innovación of Spain (grant
BFU2008-03154/BMC) and by the Generalidad Valenciana (ACOMP/2010/278) to R.F, by
the National Science Foundation of the USA (grant IRFP-0602042) to D.G, and by the
Agencia Española de Cooperación Internacional (A/022313/08) to A.E. Due to space
limitations we have been unable to refer to the original work of many authors and, instead,
we have recurred to reviews. We apologize for any inconvenience this may have caused.Peer reviewe
Separate Contribution of Striatum Volume and Pitch Discrimination to Individual Differences in Music Reward
Individual differences in the level of pleasure induced by music have been associated with the response of the
striatum and differences in functional connectivity between the striatum and the auditory cortex. In this study, we
tested whether individual differences in music reward are related to the structure of the striatum and the ability to
discriminate pitch. We acquired a 3-D magnetization-prepared rapid-acquisition gradient-echoimage for 32 musicians
and 26 nonmusicians who completed a music-reward questionnaire and a test of pitch discrimination. The analysis
of both groups together showed that sensitivity to music reward correlated negatively with the volume of both the
caudate and nucleus accumbens and correlated positively with pitch-discrimination abilities. Moreover, musicianship,
pitch discrimination, and caudate volume significantly predicted individual differences in music reward. These results
are consistent with the proposal that individual differences in music reward depend on the interplay between auditory
abilities and the reward network