The structures of the 5′ termini of the protamine mRNAs (PmRNAs) have been investigated by inhibiting their translation in wheat-germ extracts in the presence of 7-methyl guanosine 5′-phosphate (m7GMP), an analogue of ‘cap’ structure in mRNAs. Second, the cap structures on PmRNAs were examined by labelling the RNA at the 5′ end with T4 polynucleotide kinase and [γ-32p]ATP before and after removal of these structures with tobacco acid pyrophosphatase and alkaline phosphatase. The results indicate that cap structures of the PmRNAs are heterogeneous. It appears that the mRNAs coding Ior protamine components CI and CIII have at least a cap 1 structure while the mRNAs coding for CII do not appear to be capped or methylated.

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