Figure 4.

Self-association of intasomes. (A) Self-association of SSCs is evident as a ladder of bands in gel electrophoresis. The extent of self-association is variable, but increases with incubation time and is greater after incubation at low ionic strength. (B) The ladder is due to self-association of assembled SSCs and not recruitment of additional protomers of integrase. When SSCs are assembled from a mixture of “short” and “long” viral DNA molecules, the first band in the ladder series splits into three (Group 1) as a result of pairing of short with short, short with long, and long with long DNA molecules. The next band in the ladder series splits into five (Group 2), consistent with self-association of two SSCs. The number of bands in the higher order members of the series cannot be unambiguously counted. (C) AFM shows that self-association occurs through the intasomes and does not involve bridging of internal regions of the viral DNA by integrase. The images on the left and middle were from a sample deposited at 500 mM NaCl, while the image on the right was from a sample deposited at 150 mM NaCl.