This virus, which uses reverse transcriptase, attacks and destroys CD4 T-cells, causing its victims to die of other diseases due to a weakened immune system.  
In absence of CDK9, transcription in this pathogen will terminate prematurely. This pathogen is targeted by drugs such as saquinavir and ritonavir. In addition to those protease inhibitors, this pathogen is also targeted by azidothymidine, which works by blocking an enzyme that facilitates replication of this pathogen's genome by synthesizing DNA from an RNA template. This virus, which uses reverse transcriptase, attacks and destroys CD4 T-cells, causing its victims to die of other diseases due to a weakened immune system.  For 10 points, name this sexually transmitted virus that causes AIDS.
In absence of CDK9, transcription in this pathogen will terminate prematurely.
Human Immunodeficiency Virus [prompt on answers such as "the AIDS virus" or "the virus that causes Acquired ImmunoDeficiency Syndrome"]