of the Gag proteins than the Pol proteins and have developed advanced systems to synthesize the required amount of each. As an example, after Gag synthesis nearly 95 percent of the ribosomes terminate translation, while other ribosomes continue translation to synthesize Gag–Pol. In the rough endoplasmic reticulum glycosylation begins and the env gene is translated from spliced mRNAs in the rough endoplasmic reticulum, into molecules of the envelope protein. When the envelope protein molecules are carried to the Golgi complex, they are divided into surface glycoprotein and transmembrane glycoprotein by a host protease. These two glycoprotein products stay in close affiliation, and they are transported to the plasma membrane after further glycosylation. It is important to note that a retrovirus must "bring" its own reverse transcriptase in its capsid, otherwise it is unable to utilize the enzymes of the infected cell to carry out the task, due to the unusual nature of producing DNA from RNA. Industrial drugs that are designed as protease and reverse-transcriptase inhibitors are made such that they target specific sites and sequences within their respective enzymes. However these drugs can quickly become ineffective due to the fact that the gene sequences that code for the protease and the reverse transcriptase quickly mutate. These changes in bases cause specific codons and sites with the enzymes to change and thereby avoid drug targeting by losing the sites that the drug actually targets. Because reverse transcription lacks the usual proofreading of DNA replication, a retrovirus mutates very often. This enables the virus to grow resistant to antiviral pharmaceuticals quickly, and impedes the development of effective vaccines and inhibitors for the retrovirus. One difficulty faced with some retroviruses, such as the Moloney retrovirus, involves the requirement for cells to be actively dividing for transduction. As a result, cells such as neurons are very resistant to infection and transduction by retroviruses. This gives rise to a concern that insertional mutagenesis due to integration into the host genome might lead to cancer or leukemia. This is unlike Lentivirus, a genus of Retroviridae, which are able to integrate their RNA into the genome of non-dividing host cells. Recombination Two RNA genomes are packaged into each retrovirus particle, but, after an infection, each virus generates only one provirus. After infection, reverse transcription occurs and this process is accompanied by recombination. Recombination involves template strand switching between the two genome copies (copy choice recombination) during