Quantitative in situ hybridization reveals extent of sequence homology between related DNA sequences in Drosophila melanogaster

Cloned DNA from the larval serum protein one (LSP-1) genes was hybridized to polytene chromosomes of D. melanogaster. The ratio of grains deposited over any two of the three LSP-1 genes with any one LSP-1 subunit probe was constant. Varying the gene dose of any one LSP-1 subunit relative to the others by up to six fold gave a linear relationship of grain ratios to gene ratios. We show that these constant ratios closely reflect the extent of sequence homology between the genes as determined by heteroduplex mapping (Smith et al., 1981) and thermal denaturation studies. The results obtained demonstrate that the LSP-1 subunit genes are present in equal copies in the genome.     

Quantitative analysis of the amount of larval serum protein-1 (LSP-1) synthesized by flies with different doses of the LSP-1 coding sequences

Larval serum protein-1 (LSP-1) and LSP-2 are the major proteins of Drosophila larval serum. The amount of LSP-1 synthesized is strictly proportional to the number of LSP-1 genes present within the range 1-10. The normal number in female flies is 6. Flies with extreme amounts of LSP-1 were, by our criteria, as fit as the wild type. The ratio of LSP-2:LSP-1 was analyzed in 169 different stocks and was constant in 164 of these. The significantly different ratios in five stocks were all due to the lack of one of the LSP-1 gene products.     

Location of the LSP-1 Genes in Drosophila Species by IN SITU Hybridization

The locations of the larval serum protein one (LSP-1) α, β and γ genes were determined in Drosophila melanogaster and in 14 other species of Drosophila by in situ hybridization to polytene chromosomes. The LSP-1 α gene mapped to bands 11B on the X chromosome, the LSP-1 β gene mapped to bands 21D-E on chromosome 2L, and the LSP-1 γ gene mapped to band 61A in all the melanogaster subgroup species. In eight other species, both the LSP-1 α and β genes mapped to one site on Muller's element E which corresponds to chromosome 3R of D. melanogaster. No hybridization of LSP-1 γ was detected in these eight species. Restriction enzyme digestion and analysis of genomic DNA by filter transfer hybridization confirmed the presence of LSP-1 α-like and β-like genes in seven of these species. These results are discussed with respect to conservation of the chromosomal elements in the genus Drosophila.