What type of ligase is specifically responsible for joining RNA fragments?

RNA ligase is specifically responsible for joining RNA fragments. This enzyme catalyzes the formation of covalent bonds between the ends of RNA molecules, effectively linking them together to create a longer RNA strand. This process is essential during RNA processing, particularly in the maturation of certain types of RNA, such as transfer RNA (tRNA) and certain viral RNAs, where fragments may need to be joined end-to-end.

In contrast, DNA ligase is an enzyme that facilitates the joining of DNA strands by forming phosphodiester bonds between nucleotides, predominantly during DNA replication and repair. Protein ligase, while it suggests a ligase function, is not a commonly recognized class of enzymes responsible for joining RNA fragments. The term "enzyme ligase" is vague and does not refer to a specific type of ligase active in RNA processing. Thus, the specificity of RNA ligase for RNA substrates establishes it as the correct choice for this question.