What is the purpose of long terminal repeats?

flanking nucleotide sequences, known as long terminal repeats (LTR), which code for double-stranded DNA that can recognize host cell DNA sequences for integration of the proviral DNA into the host cell chromosome.

What are the functions of the proviral LTR sequences in a retrovirus life cycle?

Once the provirus has been integrated, the LTR on the 5′ end serves as the promoter for the entire retroviral genome, while the LTR at the 3′ end provides for nascent viral RNA polyadenylation and, in HIV-1, HIV-2, and SIV, encodes the accessory protein, Nef.

What is long terminal repeat promoter?

Long Terminal Repeats: The Retroviral Promoter. The long terminal repeat (LTR) is the control center for gene expression.

What is the normal function of a LTR?

The LTRs are necessary and sufficient for promoter activity and transcription of the retroelement. Functional features common to LTRs include: 5′ TG and 3′ CA dinucleotides necessary for integration into the host genome; Pol II promoter elements and a transcription start site; and a polyadenylation and cleavage signal.

What is U3 and U5?

Each consists of three “domains.” U3 and U5 are derived from unique sequences at the 3′ and 5′ termini of the viral RNA genome, respectively, and R denotes repeat sequences of the termini whose homology is exploited to transfer nascent DNA within or between genomes during proviral DNA synthesis.

What are inverted repeat sequences?

An inverted repeat (or IR) is a single stranded sequence of nucleotides followed downstream by its reverse complement. These repeated DNA sequences often range from a pair of nucleotides to a whole gene, while the proximity of the repeat sequences varies between widely dispersed and simple tandem arrays.

Why are lentiviruses used?

Gene therapy vectors derived from lentiviruses offer many potentially unique advantages over more conventional retroviral gene delivery systems. Principal amongst these is their ability to provide long-term and stable gene expression and to infect non-dividing cells, such as neurons.

What is the difference between LTR and non LTR retrotransposons?

LTR retrotransposons move by first being transcribed into RNA, followed by reverse transcription leading to a DNA copy that recombines with genomic DNA. Non-LTR retrotransposons move through a somewhat different RNA-mediated event, discussed below (Eickbush and Malik, 2002).

What is the U3 region?

The U3 region of human and simian immunodeficiency viruses (HIV and SIV, respectively) contains the basal promoter (nt −78 to −1), a core enhancer (nt −105 to −79) and a very long modulatory region (nt −454 to −104) (Gaynor, 1992).

What is the role of the inverted repeats in terminating transcription?

When rho-factor reaches the RNAP, it causes RNAP to dissociate from the DNA, terminating transcription. The inverted repeat forms a stable stem loop structure in the RNA, which causes the RNA to dissociate from the DNA template.

What is the direct repeat sequence?

Direct repeats are a type of genetic sequence that consists of two or more repeats of a specific sequence. In other words, the direct repeats are nucleotide sequences present in multiple copies in the genome. Generally, a direct repeat occurs when a sequence is repeated with the same pattern downstream.