The Metabolism of Messenger RNA Synthesized after Primary Immunization

Summary The synthesis of RNA in rat spleen cells was stimulated by immunization. Analyses of the RNA associated with ribosomes extracted from these cells which had been immunized 24 hr previously, revealed that during the 1st hr after injection of P32, the RNA synthesized in greatest amounts had messenger-like sedimentation characteristics. Over the next 24 hr, there was an extensive accumulation of stable ribosomal RNA, but the messenger RNA accumulated relatively slowly. The base composition of the 6 to 12 S RNA, measured from the P32 distribution in the various nucleotides, differed from the nucleotide composition of ribosomal and soluble RNA, and resembled more closely that of DNA in the GMP + CMP to AMP + UMP ratios. Particularly high UMP:AMP ratios also characterized this RNA. The base ratios of the messenger RNA which accumulated were different from those of the rapidly labeled but unstable 6 to 12 S RNA. On the basis of these results, it is apparent that the synthesis of at least two major species of messenger RNA are stimulated by immunization. One species is labile and may code for structural proteins and enzymes. One other is relatively stable and may be the message for antibody synthesis.