Genetics of Retroviruses - Essay Example

The core contains two identical copies of the single stranded RNA genome. The RNA molecules are complexed with reverse transcriptase and tRNA. Other viral proteins like integrase are also components of the virion particle. The outer envelope glycoprotein (SU), is the major antigen of the virus, and is responsible for receptor binding. The trans-membrane glycoprotein (TM), holds the SU protein in the envelope, and is responsible for membrane fusion “All retrovirus genomes consist of two molecules of RNA, which are s/s, (+)sense and have 5 cap and 3 poly-(A) (equivalent to mRNA).

These vary in size from ~8-11kb. Retrovirus genomes have 4 unique features: These two molecules are physically linked as a dimer by hydrogen bonds (co-sediment). In addition, there is a 3rd type of nucleic acid present in all particles, a specific type of tRNA (usually trp, pro or lys) - required for replication.” Gene order in all retroviruses is invariant: 5 - gag - pol - env - 3. The gag (group-specific antigen, core protein) gene encodes proteins that make up the nucleocapsid of the virus as well as a matrix layer, the two of which surround the RNA.

The pol gene (RNA-dependent DNA polymerase) encodes three proteins, reverse transcriptase, which copies the RNA into DNA, integrase, which integrates the DNA into the host chromosome and protease, a protein that cleaves the Gag-Pol polyprotein into smaller protein products. The env gene encodes the envelope glycoproteins. “Some retroviruses have incorporated viral oncogene sequences.”( www.bookrags.com) The genomes of complex retroviruses, such as human T-cell lymphotropic virus (HTLV) contain additional genes (e.g., tax and rex) for regulatory proteins.

R Region: A short (18-250nt) sequence which forms a direct repeat at the both ends of the genome, which is therefore terminally redundant.U5: A unique, non-coding region of 75-250nt