Studies on the heterogeneity of the 5′ ends of the protamine mRNAs from rainbow trout testis

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 C_I and C_III have at least a cap 1 structure while the mRNAs coding for C_II do not appear to be capped or methylated.