A Study of Retroviruses

            
             A cloning vector is any piece of DNA molecule taken from either virus, plasmid or cells of higher organisms in which the foreign gene can be inserted for cloning in host organism thus used as carrier.
             WHAT IS A RETROVIRUS?.
             Retrovirus is a group of viruses that belong to the family retroviridae and has genetic material in the form of RNA.
             TYPES OF RETROVIRUSES.
             There are 3 main types of retroviruses given below.
             A)ONCOVIRUSES-they are cancer causing viruses eg-mouse mammary tumour virus,human T-lymphotrophic virus.
             B)LENTIVIRUSES-they cause slow onset of disesases,they require more time for incubation eg-HIV.
             C)SPUMAVIRUSES-they do not cause any clinical disorders in human beings. Eg-human foamy virus.
             BASIC STRUCTURE OF RETROVIRUS.
             Retrovirus is a enveloped virus.
             It has a diameter of about 80-100 nanometers.
             The RNA genome is approximately 7-12 kilobases linear and single stranded.
             The genome consist of two identical copies and is associated with nuclear capsid.
             Nuclear capsid protects the genome.
             This nuclear capsid is surrounded by a capsid which protects the core.
             Also enclosed by the capsid are the enzymes like integrase,reverse transcriptase and protease.
             The capsid is the surround by a shell composed mainly of the matrix it lines the envelope.
             Finally the viral envelope forms the outermost layer and composed of two sub units mainly-.
             Surface protein-it binds to the receptor of the host cell.
             Transmembrane protein-it fuses with the host cell thus allowing matrix and capsid to be inserted.
             GENOMIC STRUCTURE OF THE RETROVIRUS.
             The RNA OF RETROVIRUS CONSIST OF CAPPED 5`end to maintain stabilty during translation.
             The 3`end has poly A tail due to addition of adenine it helps the RNA to be more stable and prevents degradation.
             The 5` LTR and 3` LTR sequence are called as long terminal repeat sequence which are present on the DNA and are repeated number of times.
             These 5`LTR sequence consist of repeated R sequence which has a promoter region and a TATA box it carries out end to end transcription, .