Translation of Vitellogenin mRNA in the Presence of 7‐Methylguanosine 5′‐Triphosphate

Messenger RNAs for total estrogenized chicken liver proteins and for two of their major constituents (vitellogenin and serum albumin), globin mRNA and Mengo virion RNA were translated in the wheat germ system and in the mRNA‐dependent reticulocyte lysate in the presence of 7‐methylguanosine 5′‐triphosphate. Protein synthesis inhibition was studied as a function of the concentration of cap analog, mRNA and translational factors. The following observations were made. (a) Synthesis directed by total poly(A)‐containing RNAs, purified vitellogenin and serum albumin mRNAs could be completely inhibited by cap analogs; messenger RNA in poysomal RNA preparations was less efficiently inhibited than purified mRNAs. (b) Monitoring immunologically translation of the population of liver messengers, vitellogenin mRNA was found to be more inhibited than serum albumin mRNA. (c) Cap analogs inhibited translation of the capped globin mRNA competitively in the wheat germ system. (d) By increasing the concentration of translational factors inhibition could be reversed. (e) Cap analogs did not inhibit translation of the uncapped Mengo virion RNA in the reticulocyte lysate but did do so, partially and not competitively, in the wheat germ system. (f) By increasing the concentration of wheat germ extract the inhibitable portion of mengo‐directed synthesis increased. These results support speculation that cap analogs compete with mRNAs on the basis of affinity for initiation complex formation. Implications regarding the behaviour of the intact reticulocyte lysate and of uncapped viral RNAs in presence of cap analog are discussed.