Wheat embryo ribonucleates. VIII. The presence of 7-methylguanosine 'cap structures' in the RNA of imbibing wheat embryos.

1. By imbibing wheat embryos in media that contain methyl-labelled methionine, it is possible to label both terminal and nonterminal 7-methylguanosine constituents in NaCl-insoluble (2.5 M, 0 degrees C) RNA (iRNA). 2. Most of the 7-[Me-14C]methylguanosine in wheat embryo i[Me-14C]RNA is present in nonterminal positions of polynucleotide chains, probably in ribosomal RNA. 3. By passage through a column of oligo-dT-cellulose, it is possible, to show that most of the 7-[Me-3H]methylguanosine in a 'bound' fraction of i[Me-3]RNA from imbibing wheat embryos is present in terminal 'cap' structures, probably in messenger RNA. 4. Although most of the 7-[Me-3H]methylguanosine in the 'unbound' (to oligo-dT-cellulose) fraction of i[Me-3H]RNA was present in nonterminal positions, there was also a highly significant fraction of 7-[Me-3H]methylguanosine in terminal 'cap' structures. Although it will be a subject of continued investigation, possible reasons why a large fraction of the total 7-[Me-3H]-methylguanosine was present in the 'unbound' fraction, in this present study, are a subject of discussion. 5. Careful analysis failed to reveal the presence of any N6,O2'-di[Me-3H]methyladenosine in the 'unbound' fraction of i[Me-3H]RNA. 6. Factors that might influence the binding of 'cap' oligonucleotides to DEAE-cellulose are the subject of a brief discussion.