Structure Of viroid And Structute of PSTV

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Structure

Viroids are composed of small, circular, single stranded RNA molecules which have some double-stranded regions. The closed single-stranded RNA circle has extensive intra-strand base pairing and interspersed unpaired loops. 

  •  They consist of a short stretch of highly complementary circular single-stranded RNA without a protein coat.
  •  The molecular weight of Viroid ranged between 85,000 and 1,30,000 daltons.
  •  Viroids are 240-380 nucleotides long and all of them have dump-bell-shaped structures.
  •  The range in size is approximately 20 nm.
  •  Viroids are catalytic RNAs (ribozymes) that cleave RNA to produce fragments containing a 5'-hydroxyl and a 2', 3'-cyclic phosphate.

Structure of PSTV: 

H.J. Cross (1979) sequenced the nucleotide sequence of the potato spindle tuber virus (PSTV). The structure of PSTVd is as follows

  • It consists of 359 ribonucleotides and is characterized by numerous intermolecular base pairing.
  • The single-stranded circular RNA makes pairing between complementary bases and the loops have no such pairing.
  • The pospiviroid has been divided into five structural/functional domains. Such as,
  1. Left terminal region/domain (TL) 
  2. Pathogenic region/domain (P) 
  3. Conserved central region/domain (CCR) 
  4. Variable region/domain (V) and 
  5. Right terminal region/domain (TR).

Fig: Simple Structure of viroid (PSTV)

Fig: Complex Structure of viroid (PSTV)

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