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Updated: Aug 12, 2026
Dissecting Host-virus Interaction in Lytic Replication of a Model Herpesvirus
Published on: October 7, 2011
Modulation of activity of Moloney murine leukemia virus preintegration complexes by host factors in vitro
L Li1, C M Farnet, W F Anderson
1Gene Therapy Laboratories, Norris Cancer Center, University of Southern California School of Medicine, Los Angeles 90033, USA.
Abstract:
We have explored the requirements for host proteins in the integration of Moloney murine leukemia virus (MoMuLV) cDNA in vitro. Following infection, it is possible to lyse cells and obtain preintegration complexes (PICs) capable of integrating the MoMuLV cDNA into an added target DNA in vitro (intermolecular integration). PICs can be stripped of required proteins by gel filtration in high-salt buffers (600 mM KCI), allowing the nature of the removed factors to be investigated by in vitro reconstitution. In a previous study of human immunodeficiency virus type 1 (HIV-1) PICs, the host protein HMG I(Y) was found to be able to restore activity to salt-stripped PICs. In contrast, salt stripping and reconstitution of MoMuLV PICs led to the proposal that a host factor is important for a different activity, blocking integration into the cDNA itself (autointegration). In this report, we investigated reconstitution of salt-stripped MoMuLV PICs and found that addition of cellular extract from uninfected NIH 3T3 cells could block autointegration and also restore intermolecular integration. Isolation of the intermolecular integration-complementing activity yielded HMG I(Y), as in the HIV-1 case. However, HMG I(Y) could not block autointegration, implicating a different host factor in this process. Additionally, when MoMuLV PICs were partially purified but not salt stripped, the intermolecular integration activity was reduced but could be stimulated by the addition of any of several purified DNA binding proteins. In summary, three activities were detected: (i) the intermolecular integration cofactor HMG I(Y), (ii) an autointegration barrier protein, and (iii) stimulatory DNA binding proteins.
Insights
Researchers identified host proteins essential for Moloney murine leukemia virus (MoMuLV) integration. They found HMG I(Y) facilitates intermolecular integration, while a distinct protein blocks autointegration, revealing key factors in viral DNA integration.
Area of Science:
- Virology
- Molecular Biology
- Host-Pathogen Interactions
Background:
- Moloney murine leukemia virus (MoMuLV) integration into host DNA is a critical step in its replication cycle.
- Preintegration complexes (PICs) mediate viral cDNA integration, and their function depends on host factors.
- Previous studies on human immunodeficiency virus type 1 (HIV-1) identified HMG I(Y) as crucial for PIC activity.
Purpose of the Study:
- To investigate the host protein requirements for MoMuLV cDNA integration in vitro.
- To identify factors involved in both intermolecular integration and autointegration of MoMuLV.
- To compare MoMuLV integration mechanisms with those of HIV-1.
Main Methods:
- Isolation and biochemical analysis of MoMuLV preintegration complexes (PICs).
- In vitro reconstitution assays using salt-stripped PICs and cellular extracts or purified proteins.
- Gel filtration chromatography to separate and identify protein factors.
- Functional assays to measure intermolecular integration and autointegration activities.
Main Results:
- Salt-stripped MoMuLV PICs required cellular extract for both intermolecular integration and blocking of autointegration.
- The host protein HMG I(Y) was identified as a cofactor that restores intermolecular integration activity.
- HMG I(Y) did not block autointegration, indicating a separate host factor is responsible for this function.
- Partially purified MoMuLV PICs showed reduced intermolecular integration, which could be stimulated by various DNA-binding proteins.
Conclusions:
- MoMuLV integration involves at least three distinct host protein activities: an intermolecular integration cofactor (HMG I(Y)), an autointegration barrier protein, and stimulatory DNA-binding proteins.
- While HMG I(Y) plays a role in MoMuLV intermolecular integration, similar to HIV-1, a different host factor is critical for preventing autointegration.
- Understanding these host factors provides insights into the regulation of retroviral DNA integration and potential therapeutic targets.
