Lengths of transcriptional units coding for the heat shock proteins in Drosophila melanogaster

Abstract

The lengths of the transcription units coding for the Drosophila melanogaster heat shock proteins were determined using the ultraviolet promoter mapping technique. The figures were in good agreement with the transcription unit lengths of three of the heat shock cytoplasmic RNA species as determined by the same technique. The rates of gene inactivation were first-order with respect to ultra-violet irradiation dose, suggesting that there are single genes of a given species in each transcriptional unit. The length of the transcription unit coding for the major heat shock protein, the 70,000 M r protein, was found to be 6.8 × 10 3 bases. The length of the transcription unit of the 2.6 × 10 3-base messenger RNA coding for the 70,000 M r protein was found to be 5.5 × 10 3 to 6.5 × 10 3 bases by two independent methods and is in good agreement with the determination for the protein. In general, the transcription units contained 3.5 to 10 times as much DNA as is needed to code for the amino acid sequence of the respective proteins. The cytoplasmic RNA transcription units were 1.5 to 6.5 times the molecular lengths of the respective RNA species. The results suggest that there is appreciable post-transcriptional cutting of the primary transcription product of these genes. The lengths of these transcription units are about one-third to one-quarter the length of DNA in an average-sized chromomere.