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Figure 5 | Retrovirology

Figure 5

From: A novel function for spumaretrovirus integrase: an early requirement for integrase-mediated cleavage of 2 LTR circles

Figure 5

Asymmetric integration is not required to understand the sequences of integrated and 2-LTR molecules observed in PFV-1 infected cells . (A) The asymmetric integration in PFV-1 virus was proposed to account for the sequences of both integrated and 2-LTR viral molecules as observed in the infected cells [24, 25]. This unusual proposed integration was able to solve the problematic lost of only 2 nucleotides between U5 extremity of the integrated molecules and the putative U5 free end, whereas the U3 end remains unchanged. This assertion was based on the following model: the linear substrate for integration is produced by two 3'-processing reactions at each end of a blunt molecule. Of note, such blunt linear molecules have never been detected in infected cells and their structure was deduced from the observed 2-LTR circles sequences. Such deduction is based on the idea that 2-LTR circles result from the ligation of blunt linear DNA. However the actors of this reaction are still unknown. (B) We propose a revised version where the PFV-1 integration remains classical. A single reaction of PFV-1 IN onto the palindrome at the LTR-LTR circle junction can generate a linear DNA with its two 3' ends processed. The subsequent integration then eliminates the two nucleotides that are lost between the observed sequences of the LTR-LTR junction and the integrated provirus.

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