Transcriptional activity at the 3' end of the actin gene at 5C on the X chromosome of Drosophila melanogaster.

Polyribosomal poly(A)+ RNA from stage-specific embryos of Drosophila melanogaster was analyzed by Northern hybridizations to determine the transcription at the 5C actin gene (act5C) and to establish whether these mRNAs are used in translation. A 3' end probe, which contains 30 nucleotides of the actin coding sequence as well as 3'-end-adjacent sequence, hybridizes in addition to the act5C transcript to a smaller transcript 450 nucleotides long. Hybridizations with the 3' end strand-specific probes show that this transcript has the same orientation as the actin gene. This transcript is temporally coexpressed with the act5C gene over most of the developmental stages examined. S1 nuclease mapping and primer extension experiments place its 5' end about 20 nucleotides upstream from the actin translation termination signal. Furthermore, the transcript appears to translate in an in vitro translation system into a protein of 7.4 kDa, as expected from the size of the open reading frame. The data suggest, but do not prove, that the 3'-end-transcribed but untranslated region of act5C may be involved in actin gene expression.