Question

34.	How is the 5´ cap added to nascent RNAs?

31.	Describe some typical features of a restriction enzyme recognition sequence.

Answer 1

34. All mRNA in case of eukaryotes have attachment of N7-methylated guanosine linked to the first nucleotide of the RNA via a reverse 5′ to 5′ triphosphate linkage. This linkage is performed by three enzymes systematically and these enzymes are RNA triphosphatase (TPase), RNA guanylyltransferase (GTase) and guanine-N7 methyltransferase (guanine-N7 MTase). RNA TPase removes the γ-phosphate from the 5′ triphosphate to generate 5′ diphosphate RNA. RNA GTase transfers a GMP group from GTP to the 5′ diphosphate via a lysine-GMP covalent intermediate. The guanine-N7 MTase then adds a methyl group to the N7 amine of the guanine cap.

31. Typical features of a restriction enzyme recognition sequence are as follows:

a. Recognition sites of type II enzymes are palindromic

b. Usually 4-8 nucleotides in length.

c. Recognition sites after cleavage can produce blunt ends or sticky ends.