References:
G.T. Montelione, B.A. Lyons, S.D. Emerson and M. Tashiro (1992) J. Am. Chem. Soc. 114 10974-10975. (Link to Article)
S. Grzesiek, J. Anglister and A. Bax (1993) J. Magn. Reson., Ser. B 101 114-119. (Link to Article)

Minimum labelling: ¹⁵N, ¹³C

Dimensions: 3

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 hydrogen nuclei, as well as on the amide nitrogen and hydrogen nuclei, resulting in a three-dimensional spectrum with one nitrogen and two hydrogen dimensions.

This is a useful spectrum for obtaining hydrogen side-chain assignments, but isn’t necessarily a must.