The human gene CCR5 is critical for HIV infection. A complex structure in its messenger RNA can cause the ribosome to slip at the area in green, making the ribosome read the remaining genetic code as nonsense RNA. This decreases the amount of CCR5 protein produced. A microRNA (miR-1224, in purple) increases stalling at that site. This causes more slippage, further reducing CCR5 production and helping to regulate the immune response.