Gene heterogeneity: a basis for alternative 5.8S rRNA processing

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Abstract
Two bands of 5.8S rRNA were observed when the total RNA isolated from rat or mouse tissue was separated by electrophoresis on high-resolution polyacrylamide gels under denaturing conditions. The minor form, with a lower mobility, represented 15-35% of the total 5.8S rRNA, depending on the source of the tissue. Sequence analysis and the kinetics of formation showed that this minor form is elongated at the 5'' end and is not a precursor. The sequence of the minor form was found to be p(C)CGAUA[CG-, 5 or 6 nucleotides longer than the major form. The minor 5.8S rRNA constitutent also formed a more stable junction complex with 28S rRNA than the shorter major sequence. The rat DNA sequence that corresponds to the additional nucelotides at the 5'' end of 5.8S rRNA was reported to be -CCGTACG-, a sequence which does not contain the extra adenylic acid residue at position 4 found in the minor form. The rodent rRNA genes are heterogeneous and the insertion of an A residue in the ribosomal precursor RNA can generate an alternate processing site.