Short intervening sequences close to the 5′ ends of the three Drosophila larval serum protein 1 genes

Abstract

The genes for the three polypeptide subunits of larval serum protein 1 (LSP1) are located at the dispersed polytene sites 11A, 22D and 61A. In order to delineate the transcription units of these genes, we have examined the structure of the S 1 nuclease resistant DNA-RNA duplexes formed between single stranded DNA and polyadenylated RNA, by two dimensional electrophoresis in native and denaturing buffers. This shows each gene to be disrupted by an intervening sequence 400 nucleotides from its 5′ end. The length of the DNA within each DNA-RNA heteroduplex structure resistant to exonuclease VII is the same as the major RNA species encoded by each gene, indicating that the intervening sequences are very short. The chromosomal segment which encodes the LSP1β gene also contains sequences complementary to a 350 nucleotide RNA molecule which is not polyadenylated. Unlike the LSP1β gene, these 350 nucleotide transcripts are not tissue specific and are found predominantly in cell nuclei rather than in the cytoplasm.