During replication, RNasel removes all of the RNA primer except the ribonucleotide directly linked to the DNA end. This is because
1
it can degrade RNA and DNA from their 5' end.
2
it can only cleave bonds between two ribonucleotides.
3
it can degrade RNA and DNA from their 3' end.
4
activity of RNasell is inhibited by the presence of duplex containing both strands as DNA.