Question

Give four different ways of how mature mRNAs are differentially regulated, and including a specific example of each

Answer 1

1.CAPPING: Capping of the pre-mRNA involves addition of 7-methylguanosine to the 5 end.Methylation of nucleotides downstream of the RNA molecule produce cap 2 and 3 structures ,in these cases the methyl groups are added to the 2'OH groups of the ribose sugar.The cap protects the 5'end of the primary RNA transcript from attack by ribonucleases that have specificity to 3'5' phosphodiester bonds.

2.Cleavage and polyadenylation:The pre-mRNA processing at the 3'end of the RNA molecule involves cleavage of its 3'end and then the addition of about adenine residues to form poly A tail.The cleavage and adenylation reactions occur if a polyadenylatiuon signal sequence is located near the 3'end of the pre mrna molecule,which is usually at the site of cleavage.

3.Splicing:The splicing reaction is catalysed by a large protein complex called spliceosome assembled from proteins and small nuclear RNA molecules that recognise the splice sites in the pre-mRNA sequence.The encoding antibodies can be splice in multiple ways to produce mature mRNA that encode different protein sequences.

4.Histone mrna processing:Histones H2A,H2B ,H3 and H4 form the core of a nucleosome and are called core histones,processing of core histone is done differently because typical histone mrNA lack several features.Thus mrna do not undergo splicing and their 3'processing is done independent of most cleavage and polyadenylation factors.