<P> In molecular biology, the five - prime cap (5 ′ cap) is a specially altered nucleotide on the 5 ′ end of some primary transcripts such as precursor messenger RNA . This process, known as mRNA capping, is highly regulated and vital in the creation of stable and mature messenger RNA able to undergo translation during protein synthesis . Mitochondrial mRNA and chloroplastic mRNA are not capped . </P> <P> In eukaryotes, the 5 ′ cap (cap - 0), found on the 5 ′ end of an mRNA molecule, consists of a guanine nucleotide connected to mRNA via an unusual 5 ′ to 5 ′ triphosphate linkage . This guanosine is methylated on the 7 position directly after capping in vivo by a methyltransferase . It is referred to as a 7 - methylguanylate cap, abbreviated m G . </P>

Which step of eukaryotic mrna processing helps in the initiation of translation