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Finally, differential effects of mutation of a residue in the C-terminal domain of integrase on concerted versus half-site integration implicate protein-protein interactions involving this domain as important for concerted integration. This suggests that nonspecific interactions of integrase with viral DNA distant from the termini contribute to the assembly of a complex that is competent for concerted integration. The first one, named 3'-processing, corresponds to a specific endonucleolytic reaction which prepares the viral DNA extremities to be competent for the subsequent covalent insertion, named strand transfer, into the. The process of integration can be divided into two sequential reactions. Longer DNA is more efficient for the concerted reaction than is shorter DNA that is capable of efficient half-site integration. Integrase, a retroviral enzyme, catalyses integration. In addition, the terminal nucleotide requirements for concerted integration are more stringent than for the half-site reaction. (PDF) Lack of Integrase Can Markedly Affect Human Immunodeficiency Virus Type 1 Particle Production in the Presence of an Active Viral Protease Lack of Integrase Can Markedly Affect Human. The reaction pathway is channeled to concerted integration, and half-site integration products are reduced with blunt-ended DNA substrate that must first be processed by integrase. In contrast, we find that blunt-ended DNA is a better substrate for the biologically relevant reaction of concerted integration of pairs of viral DNA ends. Preprocessed DNA substrates are more efficient substrates for half-site reactions than are blunt-ended substrates, which require the removal of two nucleotides prior to integration. Under most reaction conditions for integration in vitro, the majority of the reaction products are "half-site" products that result from integration of only one viral DNA end into one strand of the target DNA. Retroviral DNA made by reverse transcription is blunt-ended, and the viral integrase protein must remove two nucleotides from each 3' end prior to integration into chromosomal DNA.