In ancient times (60's and 70's) ----------------

In the original Roman system, the mini-Roman opening was 2C to show exactly any 4-4-4-1 shape with 12-16 hcp. With a weak hand, responder signed off; and if opener is short in that suit, opener bids the next step. With a strong, game-forcing hand, responder uses a 2N response to ask for the singleton.

The modern convention ---------------------

Because most modern systems use 2C for some other meaning (eg in Standard American it's used for the strong opening, and in Big Club systems it's used for a natural club hand), the adopted mini-Roman convention is the 2D opening to show any 4-4-4-1 hand with 11-15 hcp (the point count is almost always lower nowadays for every convention). Some players also include 5-4-4-0 hands where the five card suit is either minor suit.

Partner responds the same way as in "ancient times:" a cheap re-bid in a suit or pass is a signoff. If responder has bid opener's singleton, opener bids the next step. With a strong hand responder bids 2N to ask for the shortness or jumps to game in a suit (which opener cannot correct).

Over interference -----------------

Handling interference is easy for responder. Responder doubles to show a cooperative penalty hand-- ie, a hand with at least three trumps. Opener leaves in the double with a four carder or takes it out if that is his singleton.