Zoe Kazan on playing her real-life boyfriend Paul Dano’s dream girl in ‘Ruby Sparks’

Mixing business with pleasure is usually not advised … particularly when it comes to relationships. But when Zoe Kazan was working on the screenplay for "Ruby Sparks," she subconsciously wrote herself and her boyfriend of five years, Paul Dano, into the lead roles. The rom-com drama is about a struggling novelist named Calvin (played by Dano) who begins to fall in love with one of his characters, his dream girl Ruby Sparks, who suddenly appears one day as the real-life version (portrayed by Kazan). And if that wasn't already too good to be true, whatever he puts down on paper, she becomes: fluent in French, miserable without him, filled with constant joy.

The idea for the story was, in part, inspired by Kazan's romance with Dano. "I had been thinking a lot about relationships and the way we define each other in relationships, and how hard it is to hold onto your identity as people become 'co-dependent' or how much we can feel defined by our partners," she tells omg!. "I was also thinking about the Pygmalion myth [a sculptor who fell in love with his own creation] and somehow I think those things all met in my head, and I came up with this. So it's sort of a metaphorical door to a very real subject."

As she began writing it in summer 2009, Kazan, who has also starred in "It's Complicated" and on HBO's "Bored to Death," didn't exactly have herself in mind to play the title role. "I was just so excited to have an idea that felt like a movie, and I could picture what that movie would be," says the 29-year-old Yale grad. "I think it's pretty rare to get an idea that lights you up, so I was just excited to have something that I was eager to write." Then, she showed the first few pages to her boyfriend, "and he asked if I was writing it for the two of us, and I guess a sort of light bulb went off in my head, like, 'Ah, indeed, that is indeed what I'm doing.'"

Dano and Kazan as Calvin and Ruby in Ruby Sparks. (Merrick Morton)The filming of "Ruby Sparks," which is currently out on DVD and Blu-Ray, was less stressful on the relationship than one would think, considering all the long hours spent on the set — only to go home and spend even more time together. "I think we're used to bouncing ideas off of each other to help with work, even when we're not working together, so it didn't seem like such a stretch at first, but then it started to," explains Kazan. "It can be hard when you're both incredibly focused on your work, and when you're working on the same thing there's this illusion that you're spending lots and lots of time together when it in fact you're spending lots and lots of time sort of next to each other. So I think when it was all over we kind of had to take stock of our relationship." And no, they didn't need to take a break from each other. "Rather [we took] a week together as Zoe and Paul, not Calvin and Ruby."

Her relationship with Dano, 28, is also serving as inspiration for her next screenplay, for which Kazan just finished the first draft. "It's a love story of some kind," she says, then, realizing her pattern, adds, "I guess it's on my brain!"

Hollywood is certainly in Kazan's blood. The daughter of screenwriters Nicholas Kazan ("Reversal of Fortune") and Robin Swicord ("The Curious Case of Benjamin Button"), and the granddaughter of three-time Oscar-winning director Elia Kazan ("On the Waterfront"), she never considered taking a stage name to pre-empt the suggestion of nepotism. "In this age of pervasive knowledge, it would be very hard to truly achieve anonymity," she admits. "To me, my last name never seemed that famous growing up. You have to understand, I went to elementary school with children whose parents had won Oscars for being movie stars. My parents, even my grandpa, they seemed like regular people compared to that. I really didn't consider it. I also think it would look like I was ashamed of my roots, which I'm not."

As independent as she is, that's not to say Kazan doesn't run ideas by her parents every now and then. "They're very helpful when I ask them to be," she says. "I'm probably childishly stubborn about this, but I try to keep as much distance between what they do and what I do as possible just because it's sticky enough feeling like you're in the same business as your parents. But they're really smart and if I hit a roadblock, it's really great to have parents who can emotionally emphasize if not directly help."