S. Grzesiek, J. Anglister and A. Bax (1993) J. Magn. Reson., Ser. B 101 114-119. (Link to Article)
Minimum labelling: 15N, 13C
Magnetisation is transferred from the side-chain hydrogen nuclei to their attached 13C nuclei. Then isotropic 13C mixing is used to transfer magnetisation between the carbon nuclei. From here, magnetisation is transferred to the carbonyl carbon, on to the amide nitrogen and finally the amide hydrogen for detection. The chemical shift is evolved simultaneously on all side-chain carbon nuclei, as well as on the amide nitrogen and hydrogen nuclei, resulting in a three-dimensional spectrum.
This is a useful spectrum for obtaining carbon side-chain assignments, but isn’t necessarily a must.