- Ribonuclease H (RNase H) is an endonuclease that specifically degrades the RNA strand of RNA-DNA hybrids, catalyzing the hydrolysis of phosphodiester bonds. It plays an essential role in various nucleic acid metabolic processes, including DNA replication, repair, and retroviral reverse transcription. RNase H is found in both prokaryotic and eukaryotic organisms and exists in multiple forms, including RNase H1 and RNase H2, which differ in structure, substrate specificity, and biological roles.
- RNase H activity is strictly dependent on divalent metal ions, typically Mg²⁺ or Mn²⁺, for catalysis. It recognizes and cleaves RNA that is hybridized to a complementary DNA strand, producing fragments with 3′-hydroxyl and 5′-phosphate termini. This specificity makes it invaluable in molecular biology applications where selective RNA degradation is required without disturbing the DNA strand.
- One of the key applications of RNase H is in second-strand cDNA synthesis during reverse transcription protocols. After the first DNA strand is synthesized from RNA by reverse transcriptase, RNase H degrades the RNA template, allowing DNA polymerase to synthesize the complementary strand. Additionally, RNase H is employed in antisense oligonucleotide technologies, where DNA-based antisense molecules bind to target RNA and recruit endogenous RNase H to cleave the RNA, reducing gene expression.
- In retroviruses, including HIV, RNase H is a functional domain of the viral reverse transcriptase enzyme complex, facilitating removal of the RNA genome after reverse transcription to allow for DNA strand synthesis and integration into the host genome.
- In summary, RNase H is a specialized endonuclease critical for the processing of RNA-DNA hybrids, with important roles in cellular nucleic acid metabolism, molecular cloning, and gene silencing strategies. Its unique substrate specificity continues to be exploited in research, diagnostics, and therapeutic development.
