Which gene is targeted in molecular assays to quantify HIV in a patient?

The gag gene is commonly targeted in molecular assays to quantify HIV because it encodes one of the core structural proteins of the virus. The genes that encode for proteins crucial to the viral structure and replication are often used in assays because they provide reliable indicators of viral load and can reflect active viral replication. The gag gene, in particular, is essential for the nucleocapsid protein which is involved in the assembly and maturation of the virus, thus making it a key target for quantification in diagnostic tests.

In contrast, the protease is an important enzyme for processing viral proteins but is less frequently targeted for quantification purposes. Hemagglutinin is a glycoprotein found in viruses like influenza, not HIV, and ctx-m refers to a gene associated with antibiotic resistance in bacterial pathogens, thus making them irrelevant for estimating HIV viral load. Targeting the gag gene allows clinicians to monitor and manage HIV infection effectively, making it the appropriate choice in this context.