If you've passed a bookstore or checked out the cover of Entertainment Weekly lately, you may be familiar with "Fifty Shades of Grey" trilogy. E.L. James' first novel is all the rage right now, but it started out as a mega-popular piece of "Twilight" fan fiction called "Master of the Universe." Seriously. The book, which now follows a clumsy, virginal brunette named Anastasia Steele as she falls for a gorgeous, auburn-haired billionaire named Christian Grey, once used the names Bella and Edward and was written with Kristen Stewart and Robert Pattinson in mind.

Unlike Bella and Edward, who don't get it on until they're married, Ana and Christian barely know each other when they begin a kinky sexual relationship in which Edward Christian is a Dominant and Ana a Submissive. Think of it as "Twilight" minus the paranormal plus the graphic sexuality of "9 1/2 Weeks" by way of the dominant-submissive romance in "Secretary."

Now that Universal and Focus have optioned the book, the question on readers' minds is whether Robsten will consider starring in the roles literally written for them. While James, who has ultimate casting control over the leads, has said she hopes unknown stars will take the parts, she surely would love Rob and Kristen to say yes. But if they don't, here's a slate of other potential Anas and Christians that could steam it up together on-screen.

ANASTASIA

Anastasia is described as a thin 21-year-old with unruly brown locks, blue eyes and a love of classic English novels like "Tess of d'Urbervilles." She's clumsy and insecure about her looks. A recent college graduate, she's never had a boyfriend.

Amanda Seyfried

Why Her: She's got that wide-eyed innocence that would make her a believably inexperienced college graduate. With a dye job and Ana's signature jeans-and-Converse ensemble, Seyfried could pass for the kind of bookish young woman who isn't aware of her beauty (she "passed" for less than gorgeous in "Big Love" and "Jennifer's Body"). Plus, she's proved that she knows how to bring the passion to her on-screen romances (with Channing Tatum in "Dear John," Shiloh Fernandez in "Red Riding Hood," and Justin Timberlake in "In Time" -- to name just a few).

Why Not: After playing Linda Lovelace in the upcoming biopic of the legendary porn star, Seyfried  might want a break from steamy material.

Emilia Clarke

Why Her: In HBO's addictive fantasy series "Game of Thrones," Clarke has already taken a journey of sexual self-discovery and personal transformation. As Daenerys Targaryen, the English actress has had to play a pubescent princess who's given to a mighty tribal ruler as his wife. Let's just say that Clarke has already played the submissive partner, and she has zero qualms about sexing it up on screen. But it's not just the steamy scenes Clarke could handle; she's a captivating actress who could nail Ana's inner conflict between wanting Christian and wanting a "normal" relationship.

Why Not: After working on "Game of Thrones," Clarke might be tired of all the kink and nudity and could prefer a kinder, gentler role that doesn't require her to take it all off for most of the movie.

Analeigh Tipton

Why Her: The America's Next Model contestant turned heads with her breakout role in "Crazy, Stupid, Love." as the smitten babysitter who sexts Steve Carell, and she once again impressed critics in Whit Stillman's quirky comedy "Damsels in Distress." Physically, Tipton has Ana's exact look: slender figure, striking blue eyes, wavy brown hair. As a bonus, she's already dealt with a boyfriend who has sexual fetishes in "Damsels."

Why Not: Still in the early stages of her film career, Tipton might not be ready for such a scintillating role.

Nina Dobrev

Why Her: The model-turned-actress is one of television's hottest young stars, and her smart and sexy turn as Elena on The CW's hit vampire soap "The Vampire Diaries" proves she could easily take on the part of book-smart but sexually naive Ana. Dobrev is no stranger to the chemistry needed to make an obsessive on-camera romance believable, and now that she's 23, no one would balk at the idea of her transitioning to a steamy "adults only" movie.

Why Not: Dobrev has yet to headline a movie, and she may not want her first starring role to be in a hard-R sexfest, especially while she's still on the teen-targeted series.

Emma Watson

Why Her: Imagine how many heads in the "Twilight" and "Harry Potter" fandoms will explode if the actress responsible for beloved swotty Hermione sheds her Hogwarts jumpers (and everything else, for that matter) to play virginal-turned-kinky Ana Steele. Since each of her film choices -- particularly "The Perks of Being a Wallflower" -- has distanced her from Rowling's universe, it's not too far-fetched to imagine her in the role (especially since she's also a 21-year-old English major in real life). The appropriately petite and brunette Watson not only looks the part, but she has also publicly stated she'd "go naked" for the right film.

Why Not: Watson might be put off by the fact that the book has direct ties to the "Twilight" series, and that unlike "Harry Potter" and "Perks," the book is not critically acclaimed.

CHRISTIAN

Christian is a 27-year-old telecom billionaire. Like Edward, he's described as the most beautiful man ever: tall, strong, muscular, and with remarkably long ... fingers. A man of the world, he plays the piano, flies helicopters and spends millions trying to feed the world. There's just one thing: he can only have BDSM sex.

Alexander Skarsgård

Why Him: He's definitely Adonis-looking and can play both sweet and aggressive well (as anyone who saw the last season of "True Blood" can attest). He'd need to dye his hair, sure, but otherwise he's exactly the kind of powerful, gorgeous man that Christian is, and he's certainly not afraid to show off his possessive side when it comes to his romantic conquests.

Why Not: At 35, he might be a smidge too old to play Christian, but otherwise he could definitely bring the heat.

Taylor Kitsch

Why Him: "John Carter" didn't work out the way Kitsch hoped, but that doesn't mean the bedroom-eyed "Battleship" actor isn't ready for a starring role in something that's more romance than swashbuckling adventure. Ever since Kitsch played the much-loved Tim Riggins on "Friday Night Lights," we've been waiting for him to play a sexy, to-die-for leading man, and he's got what it takes to transform Christian from page to screen.

Why Not: Since "John Carter" was such a high-profile disaster, Kitsch might want to appear in a few more ensembles before jumping into a risky role.

Ryan Gosling

Why Him: If those "Hey girl" memes are any indication, Gosling is already the object of many women's desire, so having him play Christian would probably offer the largely female fandom of the series some wish fulfillment. He's already played a super sexy ladies man ("Crazy, Stupid, Love.") and an attentive lover ("Blue Valentine"), and we bet Mr. Method would make a wonderfully intense Christian.

Why Not: He's one of the most coveted actors in Hollywood with a pedigree of prestigious movies, so he might consider the source material too trashy for his standards.

Chris Hemsworth

Why Him: We loved him in "Thor" and think any actor who can make just one kiss that swoony could work wonders with  an entire film filled with memorably hot scenes. Since Christian is supposed to have a "Greek god"-like body, Hemsworth beautifully fits James' description of her complicated love interest. He's fierce, fine and fabulous -- but whether  he'd be willing to do the R-rated sequences is another question entirely.

Why Not: He's a superhero type of actor, and he may not be interested in changing his trajectory from big-budget summer blockbusters to a risque romance.

Michael Fassbender

Why Him: Perhaps you haven't seen "Shame," but the guy can portray sexual dysfunction, and he can do it in a mesmerising manner that humanizes his character. If there's any attractive, seductive actor who could inhabit the role of a man who can't have regular "vanilla sex," it's Fassbender. There's no doubt he could play a classy, educated young businessman with secret proclivities, it's just a matter of whether he would want the part.

Why Not: Like Skarsgård, Fassbender is a few years older than Christian, and he's probably not interested in a movie that started out as "Twi"-fic. But still, we can dream.