It comes as little surprise that Our Idiot Brother, Jesse Peretz’s low-key comedy about three crisis-prone sisters perpetually irritated by their free-spirited brother, is at least partially autobiographical.

Written by his sister, Evgenia, and her husband David Schisgall, the movie features bits and pieces of real life sprinkled into the fiction: Career-driven sister Miranda – a dirt-digging Vanity Fair writer played by Elizabeth Banks – works at the same magazine where Evgenia has served as a contributing editor since 1999. (Her only concession to VF, mandated by editor Graydon Carter, was that Miranda adhere to some degree of journalistic integrity.)

The director declines to say how much of Brother reflects Jesse and Evgenia’s off-screen family dynamic – on the surface, he seems a far cry from Ned, the cheerfully disheveled layabout portrayed by Paul Rudd – but the story is universal enough that it struck a chord with the actors, particularly Banks. “It’s fairly biographical for me, too,” she says. “After I read the movie, I was laughing – like, did [Jesse] somehow go to my home?

“I am the oldest, bossiest daughter [in] a family of four, with two sisters, one of whom is a divorced mother of two, and one of whom lives in Brooklyn with four roommates – she actually just moved in with her boyfriend, so we’re really hopeful he’s the one. And I have a 26-year-old brother who sells pizzas… and maybe something else.”

Banks, 37, admits she related to Miranda but also to Ned, the black sheep of his family, whose unfiltered honesty lays bare a closet full of skeletons. The difference, of course, is that Ned knows not the effects of his candor. He wanders through life spilling secrets and spreading salacious gossip, without a hint of malice or ulterior motive. He is inherently forthright, to a fault.

Likewise, Banks means no harm. The Zack and Miri Make a Porno star is refreshingly outspoken, and makes no apologies for it, but she knows what she’s doing, even when her opinions reach unexpected recipients in cyberspace.

“I once forwarded my middle sister – who married a not-great guy – and basically I was like, ‘When we go to the wedding, we're just going to make the best of a bad situation.’ My sister ended up on the e-mail forward and wrote me back, reply-all, ‘I really wish I didn't know this was how you were coming to my wedding.’

“Needless to say, I was not in the wedding, nor was my other sister. But it's all worked out. We're all best friends, and that dude is no longer in our fucking life. So I was right.”

Our Idiot Brother opens Friday at the Century 9 in San Francisco, the Century 20 in Daly City and the Regal Jack London in Oakland.For tickets and showtimes, click here.