Inside the capsid are two copies of the viral RNA, bound to each other at the dimer initiation site (DIS). Associated with the RNA is the viral NC protein (shown red below). Also inside the capsid are the viral enzymes reverse transcriptase (RT), protease (PR), and integrase (IN), which are discussed in more detail below. These are the major virus-encoded structural proteins comprising HIV particles. However, there are several further proteins encoded by lentiviruses (Table 1), and these too can be detected in particles in some cases. In addition, various host cell RNAs and proteins have been detected in HIV particles. Some of these may be captured by chance as viral particles bud out of infected cells. Others may be captured more selectively and assist in viral replication, such as the tRNA(Lys3) RNA primer used to initiate reverse transcription.