Reverse transcriptase
Stavudine is a nucleoside analog of thymidine. It is phosphorylated by cellular kinases into an active triphosphate. Stavudine triphosphate inhibits HIV's reverse transcriptase by competing with the natural substrate, thymidine triphosphate. Reverse transcriptase is the enzyme the virus uses to make a DNA copy of its RNA in order to insert its genetic material into the host's DNA. Upon incorporation into the DNA strand, stavudine triphosphate causes termination of DNA replication.