An active variant of the prokaryotic transposable element IS903 carries an amber stop codon in the middle of an open reading frame

Summary A nematode mutant lacking pheromone activity does not enter the developmentally arrested dispersal stage called the dauer larva unless exogenous pheromone is added to the growth medium, indicating that the pheromone is required for wild-type dauer larva formation. In contrast, a class of temperature-sensitive mutant forms dauer larvae even in the absence of detectable pheromone, indicating that such mutants bypass the normal pheromone requirement. A rapid bioassay of pheromone produced by individual nematodes has been developed for genetic analysis of pheromone production.