EcoRI is a restriction endonuclease enzyme isolated from Escherichia coli strain RY 13. It cuts double-stranded DNA specifically at the palindromic recognition sequence $5'-\text{GAATTC}-3'$.

Each thermal cycle of polymerase chain reaction (PCR) consists of three successive steps:

• Denaturation: Separation of dsDNA strands by heating at $94-96^\circ\text{C}$.
• Annealing: Binding of oligonucleotide primers to single strands at $50-60^\circ\text{C}$.
• Extension: Primer extension by Taq DNA polymerase at $72^\circ\text{C}$.
  
  'Propagation' is not a step in PCR. Hence, (A), (B) and (D) only are correct (Option 1).

The first restriction endonuclease discovered and characterized was Hind II, isolated from Haemophilus influenzae Rd. Its functioning depended on a specific 6-base pair nucleotide sequence recognized five years later.

After completion of the biosynthetic stage (fermentation in bioreactors), the product has to be subjected through a series of processes before it is ready for marketing as a finished product. The processes include separation and purification, which are collectively referred to as downstream processing.