Final answer:
The stability of pre-tRNAs and pre-rRNAs is mainly enhanced through methylation. This modification serves to stabilize the RNA molecules, complementing other processing steps such as 5' capping, which is significant for pre-mRNA.
Step-by-step explanation:
The processing step that enhances the stability of pre-tRNAs and pre-rRNAs is methylation. This modification occurs at various sites within these RNA molecules and serves to stabilize their structure, helping to prevent degradation. Notable among these processing steps are 5' capping of pre-mRNA, where a 7-methylguanosine cap is added, which not only protects the mRNA from degradation but also aids in the initiation of translation by ribosomes. However, for pre-tRNAs and pre-rRNAs specifically, methylation plays a critical role in their processing and stabilization, alongside other modifications like intramolecular cleavage and nucleotide conversions.