These days, Sarah Nathan gets to do something not a lot of sisters get to do: Run headlong into her brother without fear of retribution.

Sarah, a senior, shares the stage with her sophomore brother, Eli, this weekend as North Salem High School presents “42nd Street,” the tap-happy musical in which newcomer Peggy Sawyer (Sarah) barrels into theatrical great Julian Marsh (Eli) – several times.

Her kid brother didn’t always have Sarah’s love of the stage. That took time and a little prodding, she says.

“He got into it because I was always into it and my mom sort of bribed him: ‘You just do it. I’ll give you Xbox if you try out,’” she recalls, adding: “He ends up getting great parts and he loves it. It’s great because he’s a boy and we need more boys doing this kind of stuff.”

The acting bug has bitten the Nathan family.

“It used to be a lot of rewards for doing this kind of stuff,” Eli says, “but it’s nicer now because I like doing it.” Then he quickly adds: “Don’t get me wrong. I still like the rewards.”

For inspiration to play Marsh, he looked no farther than to director Jennifer Ryan.

“She’s got a very loud voice, a lot of stage presence,” he says. “He’s a lot like her, in a good way. She moves with purpose.” That’s something Eli hopes to do as Marsh – move with purpose – something he says he rarely does when he’s not on stage. (“I tend to shift my weight from side to side a lot,” he says.)

Director Ryan sees established and emerging ability in her young stars.

“Her enthusiasm for theater has really worn off on him,” says Ryan. “He’s quite a talented kid, he really is. Her talent is obvious but his is building and he’s really learning how to hold stage and do it all himself. I’m very proud of him. And they’re both hard workers.”

“42nd Street,” the musical based on the 1933 film, is full of toe-tapping songs, from “We’re in the Money” to “Lullaby of Broadway” to the title song, in which the star invites all to “Come and meet those dancing feet on the avenue I’m taking you to, 42nd Street.”

Ryan says this musical is a fitting farewell to her seniors who, six years ago, were the youngest members of the cast of “Bye Bye Birdie,” a show that revived musicals at North Salem after a 15-year hiatus.

Ryan and choreographer Barbara Rue wanted to give their senior girls, dancers all, a chance to shine. And “42nd Street” fit the bill.

“Barbara got so close to them, so we needed to send them out tapping — and hopefully the audience whistling and singing and tapping their toes.”

Is it difficult for Sarah to take orders from her little brother?

“That’s really hard because I definitely boss my brother around. But recently, he’s much bigger than I am. I can’t boss him around anymore. It’s become a problem,” she says with a broad smile.

“We get along better now that I’m bigger,” Eli agrees. “It’s more equal.”

Sarah’s a dancer, so the tap routines weren’t too taxing. Nor was getting into character to play the innocent Peggy: Sarah says she looked to her cast.

“I’m really close to all the little girls in the show, so it’s really easy to draw inspiration, to relate,” she says.

Having a sibling in the show is a definite advantage, Eli says.

“Not a lot of people have a brother or sister in the show, so it helps out a lot when we’re practicing our lines,” he says. Sarah gave him pointers about how to stand, how to not point so much, how to project his voice more.

“She’s there to make sure I don’t get too sloppy,” he says.

Sarah hopes to study musical theater in college next year – although she’s not exactly sure where, yet. She’s been on several auditions at which she finds she’s in the same boat as the character she’ll play this weekend: Trying to break into show business.

“Peggy is very naive and young, so hopefully I’ll be more worldly wise than she is,” Sarah says. “I’ve struggled in the past year determining whether this is the right career for me to choose and if I should look somewhere else. Because there’s no guarantees for this kind of work, but it’s what I want to do. I’m very lucky to know what I want to do.”

Eli knows what he’ll have to do next year when the musical rolls around, with or without the promise of Xbox: “With her not there, I’ll need to learn to fly on my own,” he says.

PHOTO (By Frank Becerra Jr./The Journal News): Siblings Eli Nathan as Julian Marsh and Sarah Nathan as Peggy Sawyer perform a scene from “42nd Street” on the stage at North Salem High School.

“42nd Street”
Where: North Salem High School, 230 June Road, North Salem.
When: 7:30 p.m. Friday and Saturday; 2 p.m. Sunday.
Tickets: $10.
Call: 914-669-5414.
With: Sam Cassano, Phoebe Coughlin, Emma Damiani, Jamie Delvecchio, Cate Devey, Sean Devey, Mackenzie Dunn, Drew Fauser, Mackensie Fauser, Camilla Fay, Phoebe Foard, Cory Gardner, Cody Garrett, Michelle Garville, Elena Gasparri, Cecilia Heffernen, Melanie Hublard Hershman, Maddie Kirshoff, Brittany Leonard, Kaitlyn Leonard, Ashley LoBuono, Samantha Marshall, Cailyn McCarthy, Megan Moore, Wendy Mumford, Erica Nagi, Eli Nathan, Sarah Nathan, Nicole Netsch, Damon Quattrochi, Anabelle Robert, Nicole Robert, Spencer Rue, Trevor Rue, Nicki Ruggi, Liam Ryan, Jillian Schumacher, Emma Sherman, Michele Teplensky, Zac Uslianer, Alexandra Walsh, Christina Walsh, Jenna Zappola, Samantha Ziegelmeier, Ty Togonon, Alex Tytla, Charlie Delker, Danny Koch, Harris Field, Johannah Acito, Elizabeth Holt, Ali Buchalter, Sabrina D’Agostino, Adrian Windus, Victoria Holt, Valerie McGovern, Alex Valentin, Mickey Jacobsen.