Notes on Genus: Crinivirus
flexuous filaments
Type member: Lettuce infectious yellows virus
Contents
General Description
This is one of three genera in the family
Closteroviridae, which are characterised by their very long (950-2000 nm) and very flexuous particles. They were previously classified as
closteroviruses but are now classified separately because they have a bipartite genome. Infected plant cells contain massive particle aggregates, often organized into banded inclusions. The name is derived from the Latin
crinis, = hair.
Morphology
Virions filamentous, not enveloped, very flexuous, 950-2000 nm long and 10-13 nm in diameter. There is a distinct virion tail. Symmetry helical, with pitch of 3.4-3.7 nm.
Virions composed of 5% nucleic acid.
Genome
Bipartite, linear, single-stranded, positive sense RNA 15,000 to 20,000 nucleotides long. There are sequences with potential hairpin structure near the 3'-end. The 3' terminus has no poly(A) tract and the 5' terminus probably has a methylated nucleotide cap.
Genus Genomic Organization
The genome organisation is broadly similar to the closteroviruses but divided between two RNAs. RNA1 has three or four ORFs, including those involved in virus replication. RNA2 has five or six ORFs, including a heat shock protein homologue and two coat proteins. The ORFs are translated from a set of overlapping, 3'-coterminal subgenomic RNAs.
Type Member Genomic Organization
The RNA is translated from eight open reading frames:
| RNA1 has 3 ORFs: |
| 1 | 217 kDa | Polyprotein ORF1a, containing a methyltransferase motif |
| 2 | 55 kDa | Polymerase ORF 1b probably expressed by ribosomal frameshift with ORF1a |
| 3 | 32 kDa | unknown function |
| RNA2 has 5 ORFs: |
| 4 | 62 kDa | heat-shock protein analogue |
| 5 | 59 kDa | unknown function |
| 6 | 28 kDa | Coat protein |
| 7 | 52 kDa | Minor coat protein |
| 8 | 26 kDa | unknown function |
