How do I initialize a Signature with the v2?#111

I have a signature without having the private key - and I want to verify that it was signed by the public key that claims the signature. I used to do : `recoverPublicKey(msg, sig, rec)` but now it has changed to `sig.recoverPublicKey(msg)`. How do I initialize the `Signature` since it seems that constructor only takes 2 big ints as params (and not a buffer/string).