As someone said Vmo in a turboprop or jet is equivalent to Vno in a piston, in that this is the speed at which the aircraft can withstand its design load limits (ie, +/- g under certification requirements, which I cannot think of at the moment).
The yellow arc, (Vno to Vne in a piston), or smooth air speed range as they call it, the aircraft is only designed to withstand a much reduced +/- g range.
So as most of the older and wiser pilots tell you, if you want to fly with the same safety margin to unexpected turbulence that turboprops and jets use, never ever fly in the yellow arc.