THE RIBOSOMAL RNA INTRONS OF CALLIPHORA ERYTHROCEPHALA AND THE CALMODULIN GENE OF DROSOPHILA MELANOGASTER (INSECTS)
SMITH, VANA LYNN
Doctor of Philosophy
The available cloned examples of the intron-28S coding sequence junctions from the rDNA of Calliphora erythrocephala have been sequenced. These introns interrupt the rDNA at the same position as the type 1 intron family first detected in D. melanogaster and D. virilis. A duplication of 14 bp of the 28S rRNA coding sequence surrounds a shortened 2.8 kb version of the major genomic length class of introns. This duplication is characteristic of the type 1 rDNA intron family in D. melanogaster and D virilis. Comparison of the intron sequences from the three Dipteran flies has revealed considerable homology between the 3' intron sequences of C. erythrocephala and D. virilis. The 28S coding sequences are highly conserved between these flies. However, a region of diverence has been located and found to correspond to the eukaryotic analogue of the L1 ribosomal protein binding site of the prokaryotic 23S rRNA. A set of overlapping phage clones representing 20.5 kb of the region surrounding the calmodulin gene of D. melanogaster has been isolated from a genomic library. Mapping of the protein coding regions suggests that the calmodulin gene is divided into four exons and three introns. Intron A has separated the initiation codon from the coding regions. Introns B and C, beween amino acids 58 and 59 and amino acids 139 and 140, respectively, split two of the four calcium binding domains. The amino acid sequence of residues 1 through 139 of calmodulin has been deduced from the DNA sequence. In comparison to the mammalian calmodulin sequences, there is a single amino acid substitution at position 99, where phenylalanine replaces tyrosine. A comparison of the D. melanogaster calmodulin gene sequences to other known calmodulin genes shows from 79% to 85% homology.