Referencing movieclips within movieclips

ok heres the problem:

I have a movieclip which is a button, and this button is inside another movie clip, and this movie clip is within the main movieclip, soo

mainMenu ----> subMenu ----> buttonMenu

how would i reference the button in buttonMenu so that when it is released it goes to requeid frame.

i tried:

_root.mainMenu.subMenu.buttonMenu.onRelease = function() {
required actions
};

but it doesn’t work. I’m sure i’m missing something pretty simple but been looking at it for ages now and its just gone blurry.

I’ve assigned al lthe movieclips instance names.

Many Thanks

Sean