The West Coast premiere of Anna Ziegler's play about the discovery of DNA, accompanied by overtones of sexism and pollution, is not an unalloyed delight, but it exemplifies everything that should make small theater in Los Angeles an inalienable right for young actors.

The Fountain Theatre's artistic team — Deborah Lawlor, Stephen Sachs and Simon Levy, director of "Photograph 51" — makes each production feel like it has been built from the ground up, not constructed from used parts or according to unchanging theatrical notions.

The result is that the actors they cast — whether seasoned professionals, young stars in the making or drifters checking out an actor's life — bring a wonderful innocence of purity and hope to their work that makes you want to stay with them until the curtain comes down. Such results are the essence of small theater in L.A. and what has earned it a special place in the hearts of professionals.

Before seeing "Photograph 51," you need to know that the three scientists who discovered that DNA is a double "not a single" helix — James Watson, Francis Crick and Maurice Wilkins — "neglected" to credit a fourth key contributor, Rosalind Franklin, whose X-ray photograph clinched their hypothesis.

Aria Alpert plays Franklin as a complex combination of deeply repressed anger sublimated into a life of poetry and intellectual discovery, showing off a disciplined but charismatic style that lets her down only when she tries to loosen up during her dalliance with a young man (Ross Hellwig, reminiscent of a young Tom Tryon).

As the three eccentrically Dickensian scientists, Ian Gould's Watson can barely keep still for his nonstop energy and charm, Kerby Joe Grubb's Crick has a laid-back Shakespearean majesty, and Daniel Billet's lovelorn Wilkins — unfortunately, Ziegler's most unconvincing character — brims over with tics, giggles and other physical idiosyncrasies. Meanwhile, Graham Norris keeps stealing the show as the uniquely engaging, unusually authentic Raymond Gosling, half medical researcher and half Greek chorus.

Director Levy's firm hand on the throttle leaves the actors little time for reflection and might conceal Ziegler's concerns more ambiguously than she intends. As always at the Fountain, the production team uses its modest budget to excellent effect.