  An increasing number of numerical simulations and experiments describing the
turbulent spectrum of Rayleigh-Taylor (RT) mixing layers came to light over the
past few years. Results reported in recent studies allow to rule out a
turbulence {\it \`a la Kolmogorov} as a mechanism acting on a self similar RT
turbulent mixing layer. A different mechanism is presented, which complies with
both numerical and experimental results and relates RT flow to other buoyant
flows.
