Particles displayed the expected viral protein composition and the modified Gag.SNAP polyprotein was efficiently processed during particle maturation . The fusion protein MA.SNAP , reactive to immunostaining with antiserum raised against HIV-1 MA as well as with anti-SNAP antiserum, was shown to be present in HIVSNAP particles, whereas two separate bands, corresponding to MA and SNAP , were detected in immunoblots of HIViSNAP samples. Electron order Everolimus micrographs of cells transfected with either wt or SNAP-tagged proviral plasmids showed viral budding profiles as well as immature and mature virions. Cells transfected with the SNAP-tagged derivative displayed a higher number of early budding structures; similar results had been obtained for an eGFP-tagged HIV derivative . Since only moderately reduced amounts of virus particles were pelleted from the supernatants of HIV wt and pCHIVSNAP transfected cells harvested at 40 h post transfection , this phenotype may be explained by delayed budding kinetics, resulting in increased numbers of budding structures detected in the steady state represented in still images. Mature HIVSNAP particles were found to display wt morphology . We then characterized the functional properties of the modified virus. The FP labeled derivative HIVeGFP had been shown to be infectious in tissue culture, but its 252917-06-9 infectivity was significantly reduced compared to wt HIV and did not sustain multiple replication rounds in tissue culture. Co-transfection of cells with an equimolar mixture of pNLCeGFP and wt pNLC4-3 results in the production of mixed particles displaying wt single-round infectivity . The introduction of other foreign sequences between the MA and CA domains yielded HIV derivatives with varying levels of infectivity, ranging from wt infectivity to a complete lack of particle production . Despite a trend towards smaller insertions generally being more favorable, we did not observe a direct correlation between the molecular mass of the inserted domain and the infectivity of the modified virus in our own studies. We compared HIVSNAP and HIViSNAP to the wt virus, as well as to mixed particles carrying approximately equimolar amounts of Gag and Gag.SNAP, respectively, with respect to the efficiency of individual replication steps .