It's a pretty far shot to say the story line in 'The Pearl' is in any way autobiographical, but as mentioned in the comment above, the story does deal with the subject of extreme loss. (Steinbeck was devastated and never really got over it when his friend was killed in an automobile accident.) The unfairness of life also comes through as another theme.
The story of 'The Pearl' actually is based on an old Mexican folk tale which had two main versions. One adheres fairly well to Steinbeck's rendition; in the second, a young pearl diver finds the pearl of great price but instead of acting wisely when he becomes rich, he squanders away his money in a very brief lapse of time. In the end, finding the pearl and not being able to deal with sudden wealth lead to his ultimate ruin.
The music and song leit motif is Steinbeck's personal contribution. The Song of the Family, the Song of the Pearl, and the Song of Evil enhance the story line by giving it a lilting, lyrical effect and are good metaphors to express the diverse thoughts and feelings of the characters.
Extra note: If you want to read a more autobiographically related work, try Steinbeck's 'Log of the Sea of Cortez.' In it he writes of some of his experiences with Ricketts while studying marine biology. (Steinbeck never finished his degree and turned to writing instead.) Also, Steinbeck or Ricketts serve as a model for the character "Doc" in his novelettes 'Cannery Row' and 'Sweet Thursday.' Later Steinbeck did a tour around the eastern half of the United States and wrote of his experiences in 'Travels with Charley.'
In a way, yes, the characters of The Pearl reveal authentic experiences of John Steinbeck. Let me explain. Specifically, John Steinbeck met an important mentor in his early life: a mentor named Edward F. Ricketts. Rickets was a marine biologist who helped shape Steinbeck's theories about humans place in creation. (I couldn't help noticing the importance of the sea as well as the priceless pearl in Steinbeck's novel. I wonder if that subject as a whole stemmed from that summer class Steinbeck took in biology at the Marine Station.) Enotes describes Steinbeck's resulting vision as thus: "man should act in concert with others to live happily and for the good of all creation." As a result, Steinbeck's characters all begin in harmony with nature but gravitate towards discord as greed takes over them. This certainly happens with Kino and results in the ultimate sadness: the death of Coyotito. Therefore, the character of Kino has its roots in the theory Steinbeck developed through his friendship with Edward F. Ricketts.