5'-Capping structures of Artemia salina mRNA and the translational inhibition by cap analogs

The mRNA of the brain shrimp Artemia salina has two types of blocked methylated 5'-terminal structures (caps). About 75% of the mRNA molecules have the 5'-end structure of m7G5'ppp5'-AmpGp and about 25% have the structure of m7G5'ppp5'GmpGp. The only other type of methylated residue found in Artemia mRNA is N6-methyladenosine and which is located at internal positions along the mRNA chain. Translation of Artemia cyst or nauplius poly(A)-rich mRNA in wheat-germ extracts was found to be inhibited by 7-methylguanosine 5'-monophosphate, a chemical analog of the cap, as well as by snythetic caps such as m7G5'ppp5'Gm. On the other hand, the elongation activity on endonegous mRNA in an Artemia cell-free system was not sensitive to 7-methylguanosine 5'-monophosphate.