Hi,

We have been carrying out an in situ proximity ligation assay (PLA) to detect the close association of two proteins on the plasma membrane of HEK293 cells. We find that the PLA signal increases when a third protein is present compared to its absence. However, we find that when oligomerisation is measured by STORM, we get evidence of association even in the absence of the third protein and no signal enhancement by the third protein.

My question: How quantitative is PLA? How well does PLA signal reflect the number of proteins in an assembled cluster? Has anyone done a quantitative comparison of PLA with other methods that measure protein associations, such as STORM?