Gag gene

More recently, various modifications have been introduced to this basic retroviral system. The inclusion of the 5 end of the gag gene is shown to enhance levels of vector production by up to 200-fold. Additionally, specific promoters have been introduced in order to attempt to control expression of the inserted gene. Most work has focused upon the use of tissue-specific promoters in an effort to limit expression of the desired gene to a specific tissue type. 

Coat proteins that make up the inner virus (core) particle. The virus gene that specifies these protein is called the gag gene. The gag gene codes for p 24, p 17 (p 18), p 9, and p 7. 

The product of the pol gene (reverse transcriptase) is translated as a larger polyprotein, on the same mRNA that is used for the gag protein alone (see Fig. 26-30). The polyprotein, or gag-pol protein, is then trimmed to the mature reverse transcriptase by proteolytic digestion. Production of the polyprotein requires a translational frameshift in the overlap region to allow the ribosome to bypass the UAG termination codon at the end of the gag gene (shaded pink in Fig. 1). 

The polymerase chain reaction is the prevalent method for DNA amplification. Much effort has been made to integrate PCR chambers on microchips to carry out amplifications of DNA molecules prior to their analysis. For instance, PCR was first achieved on a Si-based reaction chamber (25 or 50 pL) integrated with a polysilicon thin-film (2500-A-thick) heater for the amplification of the GAG gene sequence (142 bp) of HIV (cloned in bacteriophage M13) [997]. 

The role of the intrinsic protease (y) in NGF processing is reminiscent of the processing of the gag gene proteins. The precursor protein... 

Yahi N, Fantini J, Flirsch I, Chermann JC. Structural variabUity of env and gag gene products from a highly cytopathic strain of HIV-1. Arch Virol. 1992 125(l-4) 287-298. 

MoLV RTase). In avian sarcoma—leukosis viruses (ASLV, e.g., myeloblastosis, leukosis, Rous sarcoma), the polyprotein precursors, Gag-Pol, are produced as a result of a translational (-1) frameshift at the gag-pol junction. In mammalian retroviruses (e.g., MoLV and HIV), however, the Gag-Pol precursor is produced via an in-frame read through of a termination codon at the end of the gag gene. 

The Gag-Pol polyprotein contains, in the order of occurrence within the precursor gag gene products (major structural proteins), protease (PRO), RTase/RNase H, and endonuclease (or integrase, IN). All known retroviral pol genes display a similar order of functional domains. Mature RTases are derived from the Gag-Pol precursor by proteolytic cleavages performed by the virion-encoded protease. In ASLV, the pol gene product consists of RTase/RNase H-IN. 

---