Genetic transformation of Drosophila melanogaster with an autonomous P element: phenotypic and molecular analyses of long-established transformed lines.

Following transformation of a Drosophila melanogaster true M strain with an autonomous P element, six lines were established and monitored for their molecular and phenotypic properties during a 4-yr period. The number of P elements increased with time in all the lines but the rate of increase differed among lines. Furthermore, degenerate elements arose in each of the lines during propagation. By the end of the 4th yr, the total number of elements in every line was similar to that of a very strong P strain.--At the phenotypic level, all of the transformed lines evolved high P activity, but only three developed complete or nearly complete regulatory ability. The other three lines attained only intermediate levels of regulation over the 4-yr period. One of these lines was particularly noteworthy. Although it contained as many as 55 P elements per genome (20 of which were potentially complete) and had extremely high P activity potential, it continued to exhibit limited regulatory ability. In addition, when females of this line were maintained at high temperatures, the ability to suppress P activity was even further diminished. A strain with this combination of molecular and phenotypic properties, in an apparently stable configuration, has not been previously described.--The results are discussed in the context of the possible role of degenerate elements in regulating P element expression.