Addendum: An essential role for Grk2 in Hedgehog signalling downstream of Smoothened

As described on page 742 of the abovementioned paper, we identified two further putative GRK2 phosphorylation sites within the mSmo CTT in addition to the 12 previously described by Chen et al (2011); regrettably however, due to an oversight in the preparation of the final version of our manuscript, we omitted to provide the following details of these sites: S698 and S748. Both of these Ser are mutated to Ala in the mSmo14A construct that we refer to. We would also like to make it clear that our mSmoSA, in which the 12 sites identified by Chen et al (2011) are mutated, is equivalent to the mSmoSA0-5 described by these authors.