In molecular biology, the five-prime 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.
Methyltransferases are a large group of enzymes that all methylate their substrates but can be split into several subclasses based on their structural features. The most common class of methyltransferases is class I, all of which contain a Rossmann fold for binding S-Adenosyl methionine (SAM). Class II methyltransferases contain a SET domain, which are exemplified by SET domain histone methyltransferases, and class III methyltransferases, which are membrane associated. Methyltransferases can also be grouped as different types utilizing different substrates in methyl transfer reactions. These types include protein methyltransferases, DNA/RNA methyltransferases, natural product methyltransferases, and non-SAM dependent methyltransferases. SAM is the classical methyl donor for methyltransferases, however, examples of other methyl donors are seen in nature. The general mechanism for methyl transfer is a SN2-like nucleophilic attack where the methionine sulfur serves as the leaving group and the methyl group attached to it acts as the electrophile that transfers the methyl group to the enzyme substrate. SAM is converted to S-Adenosyl homocysteine (SAH) during this process. The breaking of the SAM-methyl bond and the formation of the substrate-methyl bond happen nearly simultaneously. These enzymatic reactions are found in many pathways and are implicated in genetic diseases, cancer, and metabolic diseases. Another type of methyl transfer is the radical S-Adenosyl methionine (SAM) which is the methylation of unactivated carbon atoms in primary metabolites, proteins, lipids, and RNA.
18S rRNA (adenine1779-N6/adenine1780-N6)-dimethyltransferase (EC 2.1.1.183, 18S rRNA dimethylase Dim1p, Dim1p, ScDim1, m2(6)A dimethylase, KIDIM1) is an enzyme with systematic name S-adenosyl-L-methionine:18S rRNA (adenine1779-N6/adenine1780-N6)-dimethyltransferase. This enzyme catalyses the following chemical reaction
23S rRNA (adenine2085-N6)-dimethyltransferase (EC 2.1.1.184, ErmC' methyltransferase, ermC methylase, ermC 23S rRNA methyltransferase, rRNA:m6A methyltransferase ErmC', ErmC', rRNA methyltransferase ErmC' ) is an enzyme with systematic name S-adenosyl-L-methionine:23S rRNA (adenine2085-N6)-dimethyltransferase. This enzyme catalyses the following chemical reaction
TRNA (adenine9-N1)-methyltransferase (EC 2.1.1.218, Trm10p, tRNA(m1G9/m1A9)-methyltransferase, tRNA(m1G9/m1A9)MTase, TK0422p (gene), tRNA m1A9-methyltransferase, tRNA m1A9 Mtase) is an enzyme with systematic name S-adenosyl-L-methionine:tRNA (adenine9-N1)-methyltransferase. This enzyme catalyses the following chemical reaction
TRNA (adenine58-N1)-methyltransferase (EC 2.1.1.220, tRNA m1A58 methyltransferase, tRNA (m1A58) methyltransferase, TrmI, tRNA (m1A58) Mtase, Rv2118cp, Gcd10p-Gcd14p, Trm61p-Trm6p) is an enzyme with systematic name S-adenosyl-L-methionine:tRNA (adenine58-N1)-methyltransferase. This enzyme catalyses the following chemical reaction
TRNA (guanine9-N1)-methyltransferase (EC 2.1.1.221, Trm10p, tRNA(m1G9/m1A9)-methyltransferase, tRNA(m1G9/m1A9)MTase, tRNA (guanine-N(1)-)-methyltransferase, tRNA m1G9-methyltransferase, tRNA m1G9 MTase) is an enzyme with systematic name S-adenosyl-L-methionine:tRNA (guanine9-N1)-methyltransferase. This enzyme catalyses the following chemical reaction
