What is the equivalent to npm's NPM_CONFIG_REGISTRY environment variable?

My company's project currently makes use of private node modules stored in gemfury. In order to successfully fetch the private modules, we make use of npm's NPM_CONFIG_REGISTRY environment variable. We're trying to switch over to using yarn (v0.17.9) but it appears that yarn does not recognize NPM_CONFIG_REGISTRY. I went through the yarn source code to try and find some equivalent to NPM_CONFIG_REGISTRY, but, from my initial look, nothing stands out. Does yarn have such an equivalent environment variable?