The mRNAs found in prokaryotes differ from that of eukaryotes in the following ways:
(i) The prokaryotic mRNAs are broken down by the ribonuclease into ribonucleotide, hence these are very short lived e.g. 2 minutes in E.coli. The short lived nature is due to changes in environmental conditions. In contrast the eukaryotic mRNAs have longer life i.e. they are metabolically more stable than the prokaryotic mRNAs.
(ii) In most of the prokaryotic mRNAs translation starts soon when the mRNAs are being transcribed on DNA template, whereas in eukaryotic mRNAs the translation process begins (in cytoplasm) when transcription process is over (in nucleus).
(iii) Most of the mRNAs of prokaryotes and bacteriophages are polycistronic i.e. contain several sites for initiation and termination of polypeptides due to the presence of several structural genes. Therefore, an mRNA molecule synthesizes more than one polypeptide chains. On the other hand, the mRNAs of eukaryotes are monocistronic i.e. contain only a single initiation and termination codons and synthesize one chain only.
(iv) A very little processing in mRNAs of prokaryotes occurs due to short time between transcription and translation. The mRNAs of eukaryotes undergo a considerable processing after being transcribed.
The mRNA processing includes:
(a) Polyadenylation (addition of 200-250 poly (A) at 3’OH end),
(b) Capping (formation of a 5′ cap at 5′ end by condensation of guanosine residues, and
(c) Methylation (addition of methyl i.e. -CH3 group to some of nucleotides)
(v) Similarly, the mRNAs of prokaryotes do not contain poly (A) at 3′ end, whereas the mRNA of eukaryotes contains 200-250 poly (A) residues at 3′ end.