P-element repressor autoregulation involves germ-line transcriptional repression and reduction of third intron splicing.

P cytotype is a regulatory state, characteristic of Drosophila P-strain females, in which P-element transposition is repressed. P cytotype is established maternally in the germ line but is also dependent on the presence of P elements in the zygote. One aspect of P cytotype involves transcriptional repression of the P-element promoter. Here, we show that transcriptional repression by P cytotype in the female germ line occurs by a general promoter-independent mechanism with heterologous promoters carried in P-element vectors. P-cytotype transcriptional repression results in low levels of pre-mRNA and a reduction in splicing of the P-element third intron (IVS3)-containing mRNA, thus causing an increase in the proportion of 66-kD repressor mRNA. Increased retention of IVS3 in P cytotype would result in an autoregulatory loop of 66-kD repressor production. This combination of germ-line transcriptional repression and splicing control provides a mechanism to maintain repression during the maternal inheritance of P cytotype. These findings suggest that transcriptional repression may play an additional role in the regulation of gene expression, namely allowing alteration of pre-mRNA splicing patterns.