Overexpression of human Vam6p (red) promotes clustering and fusion of lysosomes (green).

Caplan et al. (page 109)find evidence that human Vam6 protein is a mammalian tethering or docking factor with the intrinsic ability to promote lysosome fusion in vivo. The protein is related to a member of a vacuole-fusion complex in budding yeast, but has a unique citron homology domain that is required for lysosome clustering and fusion. Although Rab7 can induce lysosome fusion in yeast, dominant-negative Rab7 does not block hVam6p activity, suggesting that the human protein operates either downstream of, or in parallel to Rab7. ▪