$5'$ capping of mRNA transcripts in eukaryotes involves the following events:
- Addition of GMP on the $5'$ end
- Removal of $\gamma$-phosphate of the triphosphate on first base at the $5'$ end
- $5'-5’$ linkage between GMP and the first base at $5'$ end
- Addition of methyl group to $N7$ position of guanine
Which one of the following is the correct sequence of events?
- P, Q, R, S
- P, R, Q, S
- Q, P, R, S
- Q, P, S, R