The Myc proteins c-Myc and N-Myc are essential for development and tissue 
homoeostasis. They are up-regulated by growth factors and transmit the signal 
for cell growth and proliferation. Myc proteins are also prominent oncogenes in 
many human tumour types. Myc proteins regulate the transcription of 
protein-encoding mRNAs and the tRNAs and rRNA which mediate mRNA translation 
into protein. Myc proteins also up-regulate translation by increasing addition 
of the 7-methylguanosine cap (methyl cap) to the 5' end of pre-mRNA. Addition of 
the methyl cap increases the rate at which transcripts are translated by 
directing RNA modifications and translation initiation. Myc induces methyl cap 
formation by promoting RNA polymerase II phosphorylation which recruits the 
capping enzymes to RNA, and by up-regulating the enzyme SAHH 
(S-adenosylhomocysteine hydrolase), which neutralizes the inhibitory by-product 
of methylation reactions. Myc-induced cap methylation is a major effect of Myc 
function, being necessary for activated protein synthesis, cell proliferation 
and cell transformation. Inhibition of cap methylation is synthetic lethal with 
elevated Myc protein expression, which indicates the potential for cap 
methylation to be a therapeutic target.