Characteristic features of Viroids

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Characteristic features of Viroids:

More than 40 viroid species and many variants have been characterized. The characteristics features of Viroids are as follows:

1) It is an infectious RNA particle.
2) Viroids are made up of small single-stranded circular RNA having 240-380 nucleotides.
3) Viroids do not contain a protein coat/capsid or an envelope.
4) It has no coding capacity because the RNA of a viroid does not have an initiation code (AUG) for protein synthesis.
5) Circular RNA molecules are capable of autonomous replication.
6) Since viroids are RNA particles, they can be inactivated by ribonuclease digestion but are resistant to proteinase K and trypsin digestion.
7) Viroid has a smaller size than viruses. Its size is approximately 20 nm.
8) Viroids require host cell DNA-dependent RNA polymerase enzyme to replicate. Use host-encoded polymerase for replication.
9) Viroids infect only higher plants (exception: hepatitis D virus in humans is similar to viroid).
10) It is mainly found in nuclei of the host cells, in some cases found in the chloroplast of the host cell.
11) It resembles with the non-expressive part of DNA or introns cut of DNA.
12) Sedimentation rate is always below 50S. e.g. the sedimentation rate of PSTV is 10S.
13) Mechanically transmitted; often seed transmitted

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